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 $31.35   6.669%   $33.4407   $33.44   $33.45   $33.40  
  Purchase #2 $222.58   7.200%   $238.6058   $238.61   $238.60   $238.60  
  Purchase #3 $86.36   11.213%   $96.0435   $96.04   $96.05   $96.00  
  Purchase #4 $233.80   5.179%   $245.9085   $245.91   $245.90   $245.90  
  Purchase #5 $107.49   11.185%   $119.5128   $119.51   $119.50   $119.50  
  Purchase #6 $232.55   13.208%   $263.2652   $263.27   $263.25   $263.30  
  Purchase #7 $36.73   3.653%   $38.0717   $38.07   $38.05   $38.10  
  7 purchase totals = $950.86       $1,034.8482   $1,034.85   $1,034.80   $1,034.80