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 $199.49   13.121%   $225.6651   $225.67   $225.65   $225.70  
  Purchase #2 $227.77   8.168%   $246.3743   $246.37   $246.35   $246.40  
  Purchase #3 $33.32   13.558%   $37.8375   $37.84   $37.85   $37.80  
  Purchase #4 $59.46   12.256%   $66.7474   $66.75   $66.75   $66.70  
  Purchase #5 $142.73   3.275%   $147.4044   $147.40   $147.40   $147.40  
  Purchase #6 $131.63   13.604%   $149.5369   $149.54   $149.55   $149.50  
  Purchase #7 $66.60   11.441%   $74.2197   $74.22   $74.20   $74.20  
  7 purchase totals = $861.00       $947.7853   $947.79   $947.75   $947.70