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 $88.81   6.378%   $94.4743   $94.47   $94.45   $94.50  
  Purchase #2 $169.94   7.375%   $182.4731   $182.47   $182.45   $182.50  
  Purchase #3 $53.85   6.426%   $57.3104   $57.31   $57.30   $57.30  
  Purchase #4 $162.51   8.440%   $176.2258   $176.23   $176.25   $176.20  
  Purchase #5 $205.54   11.731%   $229.6519   $229.65   $229.65   $229.70  
  Purchase #6 $77.78   13.663%   $88.4071   $88.41   $88.40   $88.40  
  Purchase #7 $173.81   13.752%   $197.7124   $197.71   $197.70   $197.70  
  7 purchase totals = $932.24       $1,026.2550   $1,026.25   $1,026.20   $1,026.30