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 $173.80   4.731%   $182.0225   $182.02   $182.00   $182.00  
  Purchase #2 $217.27   6.244%   $230.8363   $230.84   $230.85   $230.80  
  Purchase #3 $136.43   5.842%   $144.4002   $144.40   $144.40   $144.40  
  Purchase #4 $110.32   13.779%   $125.521   $125.52   $125.50   $125.50  
  Purchase #5 $235.32   10.717%   $260.5392   $260.54   $260.55   $260.50  
  Purchase #6 $14.70   13.761%   $16.7229   $16.72   $16.70   $16.70  
  Purchase #7 $83.75   11.535%   $93.4106   $93.41   $93.40   $93.40  
  7 purchase totals = $971.59       $1,053.4527   $1,053.45   $1,053.40   $1,053.30