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 $93.94   8.511%   $101.9352   $101.94   $101.95   $101.90  
  Purchase #2 $195.48   4.570%   $204.4134   $204.41   $204.40   $204.40  
  Purchase #3 $200.77   9.281%   $219.4035   $219.40   $219.40   $219.40  
  Purchase #4 $153.83   10.557%   $170.0698   $170.07   $170.05   $170.10  
  Purchase #5 $138.67   12.750%   $156.3504   $156.35   $156.35   $156.40  
  Purchase #6 $165.86   7.843%   $178.8684   $178.87   $178.85   $178.90  
  Purchase #7 $44.51   4.678%   $46.5922   $46.59   $46.60   $46.60  
  7 purchase totals = $993.06       $1,077.6329   $1,077.63   $1,077.60   $1,077.70