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 $226.97   3.107%   $234.022   $234.02   $234.00   $234.00  
  Purchase #2 $88.52   7.278%   $94.9625   $94.96   $94.95   $95.00  
  Purchase #3 $135.96   12.829%   $153.4023   $153.40   $153.40   $153.40  
  Purchase #4 $207.77   11.205%   $231.0506   $231.05   $231.05   $231.10  
  Purchase #5 $202.54   9.171%   $221.1149   $221.11   $221.10   $221.10  
  Purchase #6 $134.74   12.281%   $151.2874   $151.29   $151.30   $151.30  
  Purchase #7 $143.49   4.348%   $149.7289   $149.73   $149.75   $149.70  
  7 purchase totals = $1,139.99       $1,235.5686   $1,235.56   $1,235.55   $1,235.60