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 $238.98   12.643%   $269.1942   $269.19   $269.20   $269.20  
  Purchase #2 $51.95   3.463%   $53.749   $53.75   $53.75   $53.70  
  Purchase #3 $129.56   8.709%   $140.8434   $140.84   $140.85   $140.80  
  Purchase #4 $6.27   6.201%   $6.6588   $6.66   $6.65   $6.70  
  Purchase #5 $181.59   11.432%   $202.3494   $202.35   $202.35   $202.30  
  Purchase #6 $59.77   3.595%   $61.9187   $61.92   $61.90   $61.90  
  Purchase #7 $204.79   6.487%   $218.0747   $218.07   $218.05   $218.10  
  7 purchase totals = $872.91       $952.7882   $952.78   $952.75   $952.70