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 $69.33   11.683%   $77.4298   $77.43   $77.45   $77.40  
  Purchase #2 $110.74   10.231%   $122.0698   $122.07   $122.05   $122.10  
  Purchase #3 $160.43   12.359%   $180.2575   $180.26   $180.25   $180.30  
  Purchase #4 $236.28   9.572%   $258.8967   $258.90   $258.90   $258.90  
  Purchase #5 $51.84   13.542%   $58.8602   $58.86   $58.85   $58.90  
  Purchase #6 $106.30   13.650%   $120.81   $120.81   $120.80   $120.80  
  Purchase #7 $91.52   7.859%   $98.7126   $98.71   $98.70   $98.70  
  7 purchase totals = $826.44       $917.0366   $917.04   $917.00   $917.10