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 $100.60   4.870%   $105.4992   $105.50   $105.50   $105.50  
  Purchase #2 $153.54   8.220%   $166.161   $166.16   $166.15   $166.20  
  Purchase #3 $170.97   11.729%   $191.0231   $191.02   $191.00   $191.00  
  Purchase #4 $177.25   13.532%   $201.2355   $201.24   $201.25   $201.20  
  Purchase #5 $28.43   10.217%   $31.3347   $31.33   $31.35   $31.30  
  Purchase #6 $88.58   5.655%   $93.5892   $93.59   $93.60   $93.60  
  Purchase #7 $33.44   7.265%   $35.8694   $35.87   $35.85   $35.90  
  7 purchase totals = $752.81       $824.7121   $824.71   $824.70   $824.70