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 $13.33   9.714%   $14.6249   $14.62   $14.60   $14.60  
  Purchase #2 $62.90   11.591%   $70.1907   $70.19   $70.20   $70.20  
  Purchase #3 $22.82   9.490%   $24.9856   $24.99   $25.00   $25.00  
  Purchase #4 $216.50   4.814%   $226.9223   $226.92   $226.90   $226.90  
  Purchase #5 $162.89   11.226%   $181.176   $181.18   $181.20   $181.20  
  Purchase #6 $114.74   5.761%   $121.3502   $121.35   $121.35   $121.40  
  Purchase #7 $115.89   11.728%   $129.4816   $129.48   $129.50   $129.50  
  7 purchase totals = $709.07       $768.7313   $768.73   $768.75   $768.80