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 $77.26   13.213%   $87.4684   $87.47   $87.45   $87.50  
  Purchase #2 $202.96   10.822%   $224.9243   $224.92   $224.90   $224.90  
  Purchase #3 $60.49   5.221%   $63.6482   $63.65   $63.65   $63.60  
  Purchase #4 $246.97   4.559%   $258.2294   $258.23   $258.25   $258.20  
  Purchase #5 $170.89   13.135%   $193.3364   $193.34   $193.35   $193.30  
  Purchase #6 $174.35   9.487%   $190.8906   $190.89   $190.90   $190.90  
  Purchase #7 $48.42   4.775%   $50.7321   $50.73   $50.75   $50.70  
  7 purchase totals = $981.34       $1,069.2294   $1,069.23   $1,069.25   $1,069.10