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 $204.64   10.291%   $225.6995   $225.70   $225.70   $225.70  
  Purchase #2 $57.73   9.713%   $63.3373   $63.34   $63.35   $63.30  
  Purchase #3 $35.66   13.706%   $40.5476   $40.55   $40.55   $40.50  
  Purchase #4 $247.72   4.685%   $259.3257   $259.33   $259.35   $259.30  
  Purchase #5 $71.89   5.145%   $75.5887   $75.59   $75.60   $75.60  
  Purchase #6 $24.25   6.257%   $25.7673   $25.77   $25.75   $25.80  
  Purchase #7 $164.37   8.334%   $178.0686   $178.07   $178.05   $178.10  
  7 purchase totals = $806.26       $868.3347   $868.35   $868.35   $868.30