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 $62.35   5.228%   $65.6097   $65.61   $65.60   $65.60  
  Purchase #2 $107.96   12.302%   $121.2412   $121.24   $121.25   $121.20  
  Purchase #3 $140.85   10.197%   $155.2125   $155.21   $155.20   $155.20  
  Purchase #4 $168.65   13.440%   $191.3166   $191.32   $191.30   $191.30  
  Purchase #5 $32.68   13.313%   $37.0307   $37.03   $37.05   $37.00  
  Purchase #6 $193.39   6.689%   $206.3259   $206.33   $206.35   $206.30  
  Purchase #7 $188.79   8.694%   $205.2034   $205.20   $205.20   $205.20  
  7 purchase totals = $894.67       $981.9400   $981.94   $981.95   $981.80