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 $193.34   13.842%   $220.1021   $220.10   $220.10   $220.10  
  Purchase #2 $174.72   11.590%   $194.97   $194.97   $194.95   $195.00  
  Purchase #3 $27.77   3.207%   $28.6606   $28.66   $28.65   $28.70  
  Purchase #4 $32.55   5.186%   $34.238   $34.24   $34.25   $34.20  
  Purchase #5 $207.49   7.856%   $223.7904   $223.79   $223.80   $223.80  
  Purchase #6 $88.45   11.769%   $98.8597   $98.86   $98.85   $98.90  
  Purchase #7 $169.88   9.844%   $186.603   $186.60   $186.60   $186.60  
  7 purchase totals = $894.20       $987.2238   $987.22   $987.20   $987.30