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 $70.39   8.344%   $76.2633   $76.26   $76.25   $76.30  
  Purchase #2 $214.84   9.604%   $235.4732   $235.47   $235.45   $235.50  
  Purchase #3 $183.57   11.741%   $205.123   $205.12   $205.10   $205.10  
  Purchase #4 $200.45   6.262%   $213.0022   $213.00   $213.00   $213.00  
  Purchase #5 $59.63   13.460%   $67.6562   $67.66   $67.65   $67.70  
  Purchase #6 $149.60   4.855%   $156.8631   $156.86   $156.85   $156.90  
  Purchase #7 $36.68   12.688%   $41.334   $41.33   $41.35   $41.30  
  7 purchase totals = $915.16       $995.7150   $995.70   $995.65   $995.80