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 $168.98   13.172%   $191.238   $191.24   $191.25   $191.20  
  Purchase #2 $85.34   11.300%   $94.9834   $94.98   $95.00   $95.00  
  Purchase #3 $27.63   7.222%   $29.6254   $29.63   $29.65   $29.60  
  Purchase #4 $43.36   5.123%   $45.5813   $45.58   $45.60   $45.60  
  Purchase #5 $134.43   4.575%   $140.5802   $140.58   $140.60   $140.60  
  Purchase #6 $36.69   3.866%   $38.1084   $38.11   $38.10   $38.10  
  Purchase #7 $213.55   13.774%   $242.9644   $242.96   $242.95   $243.00  
  7 purchase totals = $709.98       $783.0811   $783.08   $783.15   $783.10