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 $214.73   13.609%   $243.9526   $243.95   $243.95   $244.00  
  Purchase #2 $181.35   5.828%   $191.9191   $191.92   $191.90   $191.90  
  Purchase #3 $33.70   5.143%   $35.4332   $35.43   $35.45   $35.40  
  Purchase #4 $185.28   7.819%   $199.767   $199.77   $199.75   $199.80  
  Purchase #5 $246.72   11.220%   $274.402   $274.40   $274.40   $274.40  
  Purchase #6 $170.54   13.475%   $193.5203   $193.52   $193.50   $193.50  
  Purchase #7 $125.56   13.551%   $142.5746   $142.57   $142.55   $142.60  
  7 purchase totals = $1,157.88       $1,281.5688   $1,281.56   $1,281.50   $1,281.60