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 $93.37   5.464%   $98.4717   $98.47   $98.45   $98.50  
  Purchase #2 $105.77   6.482%   $112.626   $112.63   $112.65   $112.60  
  Purchase #3 $76.33   3.166%   $78.7466   $78.75   $78.75   $78.70  
  Purchase #4 $65.95   4.229%   $68.739   $68.74   $68.75   $68.70  
  Purchase #5 $173.55   4.287%   $180.9901   $180.99   $181.00   $181.00  
  Purchase #6 $186.39   12.740%   $210.1361   $210.14   $210.15   $210.10  
  Purchase #7 $102.27   7.516%   $109.9566   $109.96   $109.95   $110.00  
  7 purchase totals = $803.63       $859.6661   $859.68   $859.70   $859.60