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 $32.66   4.856%   $34.246   $34.25   $34.25   $34.20  
  Purchase #2 $226.77   3.435%   $234.5595   $234.56   $234.55   $234.60  
  Purchase #3 $50.94   6.299%   $54.1487   $54.15   $54.15   $54.10  
  Purchase #4 $138.52   6.262%   $147.1941   $147.19   $147.20   $147.20  
  Purchase #5 $152.35   8.253%   $164.9234   $164.92   $164.90   $164.90  
  Purchase #6 $71.34   3.257%   $73.6635   $73.66   $73.65   $73.70  
  Purchase #7 $236.76   7.796%   $255.2178   $255.22   $255.20   $255.20  
  7 purchase totals = $909.34       $963.9530   $963.95   $963.90   $963.90