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 $163.85   13.366%   $185.7502   $185.75   $185.75   $185.80  
  Purchase #2 $27.35   4.534%   $28.59   $28.59   $28.60   $28.60  
  Purchase #3 $20.37   12.570%   $22.9305   $22.93   $22.95   $22.90  
  Purchase #4 $48.54   11.673%   $54.2061   $54.21   $54.20   $54.20  
  Purchase #5 $78.39   6.363%   $83.378   $83.38   $83.40   $83.40  
  Purchase #6 $43.79   13.495%   $49.6995   $49.70   $49.70   $49.70  
  Purchase #7 $212.79   11.506%   $237.2736   $237.27   $237.25   $237.30  
  7 purchase totals = $595.08       $661.8279   $661.83   $661.85   $661.90