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 $24.78   4.692%   $25.9427   $25.94   $25.95   $25.90  
  Purchase #2 $99.73   11.196%   $110.8958   $110.90   $110.90   $110.90  
  Purchase #3 $215.78   3.814%   $224.0098   $224.01   $224.00   $224.00  
  Purchase #4 $113.35   6.787%   $121.0431   $121.04   $121.05   $121.00  
  Purchase #5 $40.29   12.368%   $45.2731   $45.27   $45.25   $45.30  
  Purchase #6 $53.43   6.470%   $56.8869   $56.89   $56.90   $56.90  
  Purchase #7 $8.87   8.301%   $9.6063   $9.61   $9.60   $9.60  
  7 purchase totals = $556.23       $593.6577   $593.66   $593.65   $593.60