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 $37.45   7.393%   $40.2187   $40.22   $40.20   $40.20  
  Purchase #2 $138.88   10.249%   $153.1138   $153.11   $153.10   $153.10  
  Purchase #3 $42.55   4.168%   $44.3235   $44.32   $44.30   $44.30  
  Purchase #4 $155.80   3.792%   $161.7079   $161.71   $161.70   $161.70  
  Purchase #5 $238.39   7.213%   $255.5851   $255.59   $255.60   $255.60  
  Purchase #6 $212.81   12.267%   $238.9154   $238.92   $238.90   $238.90  
  Purchase #7 $174.67   12.825%   $197.0714   $197.07   $197.05   $197.10  
  7 purchase totals = $1,000.55       $1,090.9358   $1,090.94   $1,090.85   $1,090.90