Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $195.52   8.811%   $212.7473   $212.75   $212.75   $212.70  
  Purchase #2 $166.77   11.594%   $186.1053   $186.11   $186.10   $186.10  
  Purchase #3 $202.54   9.577%   $221.9373   $221.94   $221.95   $221.90  
  Purchase #4 $94.67   6.343%   $100.6749   $100.67   $100.65   $100.70  
  Purchase #5 $189.35   10.548%   $209.3226   $209.32   $209.30   $209.30  
  Purchase #6 $200.88   7.776%   $216.5004   $216.50   $216.50   $216.50  
  Purchase #7 $114.87   12.868%   $129.6515   $129.65   $129.65   $129.70  
  7 purchase totals = $1,164.60       $1,276.9393   $1,276.94   $1,276.90   $1,276.90