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 $109.97   13.836%   $125.1854   $125.19   $125.20   $125.20  
  Purchase #2 $41.79   10.188%   $46.0476   $46.05   $46.05   $46.00  
  Purchase #3 $221.52   7.547%   $238.2381   $238.24   $238.25   $238.20  
  Purchase #4 $165.76   7.551%   $178.2765   $178.28   $178.30   $178.30  
  Purchase #5 $25.83   13.791%   $29.3922   $29.39   $29.40   $29.40  
  Purchase #6 $193.49   13.623%   $219.8491   $219.85   $219.85   $219.80  
  Purchase #7 $227.63   8.850%   $247.7753   $247.78   $247.80   $247.80  
  7 purchase totals = $985.99       $1,084.7642   $1,084.78   $1,084.85   $1,084.70