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 $83.48   11.213%   $92.8406   $92.84   $92.85   $92.80  
  Purchase #2 $212.99   13.500%   $241.7437   $241.74   $241.75   $241.70  
  Purchase #3 $151.87   3.683%   $157.4634   $157.46   $157.45   $157.50  
  Purchase #4 $149.39   7.307%   $160.3059   $160.31   $160.30   $160.30  
  Purchase #5 $88.90   7.341%   $95.4261   $95.43   $95.45   $95.40  
  Purchase #6 $138.93   6.684%   $148.2161   $148.22   $148.20   $148.20  
  Purchase #7 $170.65   12.260%   $191.5717   $191.57   $191.55   $191.60  
  7 purchase totals = $996.21       $1,087.5675   $1,087.57   $1,087.55   $1,087.50