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 $175.63   8.605%   $190.743   $190.74   $190.75   $190.70  
  Purchase #2 $134.56   9.861%   $147.829   $147.83   $147.85   $147.80  
  Purchase #3 $103.52   7.587%   $111.3741   $111.37   $111.35   $111.40  
  Purchase #4 $116.92   7.663%   $125.8796   $125.88   $125.90   $125.90  
  Purchase #5 $213.47   3.473%   $220.8838   $220.88   $220.90   $220.90  
  Purchase #6 $189.95   10.480%   $209.8568   $209.86   $209.85   $209.90  
  Purchase #7 $13.37   4.491%   $13.9704   $13.97   $13.95   $14.00  
  7 purchase totals = $947.42       $1,020.5367   $1,020.53   $1,020.55   $1,020.60