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 $111.46   6.637%   $118.8576   $118.86   $118.85   $118.90  
  Purchase #2 $207.98   6.146%   $220.7625   $220.76   $220.75   $220.80  
  Purchase #3 $232.58   9.707%   $255.1565   $255.16   $255.15   $255.20  
  Purchase #4 $131.56   8.833%   $143.1807   $143.18   $143.20   $143.20  
  Purchase #5 $113.43   9.278%   $123.954   $123.95   $123.95   $124.00  
  Purchase #6 $46.93   12.393%   $52.746   $52.75   $52.75   $52.70  
  Purchase #7 $200.28   11.334%   $222.9797   $222.98   $223.00   $223.00  
  7 purchase totals = $1,044.22       $1,137.6370   $1,137.64   $1,137.65   $1,137.80