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 $190.82   4.637%   $199.6683   $199.67   $199.65   $199.70  
  Purchase #2 $103.73   6.366%   $110.3335   $110.33   $110.35   $110.30  
  Purchase #3 $118.93   12.832%   $134.1911   $134.19   $134.20   $134.20  
  Purchase #4 $126.51   8.758%   $137.5897   $137.59   $137.60   $137.60  
  Purchase #5 $189.95   6.328%   $201.97   $201.97   $201.95   $202.00  
  Purchase #6 $31.62   7.827%   $34.0949   $34.09   $34.10   $34.10  
  Purchase #7 $124.73   6.259%   $132.5369   $132.54   $132.55   $132.50  
  7 purchase totals = $886.29       $950.3844   $950.38   $950.40   $950.40