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 $33.58   10.704%   $37.1744   $37.17   $37.15   $37.20  
  Purchase #2 $232.97   11.748%   $260.3393   $260.34   $260.35   $260.30  
  Purchase #3 $201.77   6.236%   $214.3524   $214.35   $214.35   $214.40  
  Purchase #4 $224.72   8.557%   $243.9493   $243.95   $243.95   $243.90  
  Purchase #5 $124.86   12.674%   $140.6848   $140.68   $140.70   $140.70  
  Purchase #6 $243.32   8.143%   $263.1335   $263.13   $263.15   $263.10  
  Purchase #7 $84.72   10.383%   $93.5165   $93.52   $93.50   $93.50  
  7 purchase totals = $1,145.94       $1,253.1502   $1,253.14   $1,253.15   $1,253.10