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 $121.72   10.234%   $134.1768   $134.18   $134.20   $134.20  
  Purchase #2 $190.54   3.544%   $197.2927   $197.29   $197.30   $197.30  
  Purchase #3 $88.42   7.867%   $95.376   $95.38   $95.40   $95.40  
  Purchase #4 $212.87   4.768%   $223.0196   $223.02   $223.00   $223.00  
  Purchase #5 $178.59   7.489%   $191.9646   $191.96   $191.95   $192.00  
  Purchase #6 $53.80   7.615%   $57.8969   $57.90   $57.90   $57.90  
  Purchase #7 $64.55   4.503%   $67.4567   $67.46   $67.45   $67.50  
  7 purchase totals = $910.49       $967.1833   $967.19   $967.20   $967.30