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 $141.46   9.117%   $154.3569   $154.36   $154.35   $154.40  
  Purchase #2 $16.89   5.168%   $17.7629   $17.76   $17.75   $17.80  
  Purchase #3 $63.56   12.494%   $71.5012   $71.50   $71.50   $71.50  
  Purchase #4 $229.64   9.842%   $252.2412   $252.24   $252.25   $252.20  
  Purchase #5 $182.29   6.787%   $194.662   $194.66   $194.65   $194.70  
  Purchase #6 $14.59   7.362%   $15.6641   $15.66   $15.65   $15.70  
  Purchase #7 $209.73   4.821%   $219.8411   $219.84   $219.85   $219.80  
  7 purchase totals = $858.16       $926.0294   $926.02   $926.00   $926.10