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 $59.54   4.179%   $62.0282   $62.03   $62.05   $62.00  
  Purchase #2 $48.57   7.339%   $52.1346   $52.13   $52.15   $52.10  
  Purchase #3 $232.26   8.427%   $251.8326   $251.83   $251.85   $251.80  
  Purchase #4 $42.76   13.844%   $48.6797   $48.68   $48.70   $48.70  
  Purchase #5 $216.73   7.476%   $232.9327   $232.93   $232.95   $232.90  
  Purchase #6 $54.78   11.794%   $61.2408   $61.24   $61.25   $61.20  
  Purchase #7 $132.58   9.690%   $145.427   $145.43   $145.45   $145.40  
  7 purchase totals = $787.22       $854.2756   $854.27   $854.40   $854.10