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 $92.48   11.549%   $103.1605   $103.16   $103.15   $103.20  
  Purchase #2 $90.86   12.429%   $102.153   $102.15   $102.15   $102.20  
  Purchase #3 $57.37   9.272%   $62.6893   $62.69   $62.70   $62.70  
  Purchase #4 $238.68   8.846%   $259.7936   $259.79   $259.80   $259.80  
  Purchase #5 $22.79   7.159%   $24.4215   $24.42   $24.40   $24.40  
  Purchase #6 $136.41   11.700%   $152.37   $152.37   $152.35   $152.40  
  Purchase #7 $169.83   11.425%   $189.2331   $189.23   $189.25   $189.20  
  7 purchase totals = $808.42       $893.8210   $893.81   $893.80   $893.90