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 $133.53   9.415%   $146.1018   $146.10   $146.10   $146.10  
  Purchase #2 $193.42   3.776%   $200.7235   $200.72   $200.70   $200.70  
  Purchase #3 $43.67   4.721%   $45.7317   $45.73   $45.75   $45.70  
  Purchase #4 $230.82   6.777%   $246.4627   $246.46   $246.45   $246.50  
  Purchase #5 $55.86   3.774%   $57.9682   $57.97   $57.95   $58.00  
  Purchase #6 $121.75   3.408%   $125.8992   $125.90   $125.90   $125.90  
  Purchase #7 $161.32   5.236%   $169.7667   $169.77   $169.75   $169.80  
  7 purchase totals = $940.37       $992.6538   $992.65   $992.60   $992.70