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 $64.82   12.552%   $72.9562   $72.96   $72.95   $73.00  
  Purchase #2 $179.96   11.186%   $200.0903   $200.09   $200.10   $200.10  
  Purchase #3 $94.67   10.437%   $104.5507   $104.55   $104.55   $104.60  
  Purchase #4 $57.52   5.661%   $60.7762   $60.78   $60.80   $60.80  
  Purchase #5 $193.47   9.316%   $211.4937   $211.49   $211.50   $211.50  
  Purchase #6 $5.87   5.422%   $6.1883   $6.19   $6.20   $6.20  
  Purchase #7 $116.35   3.478%   $120.3967   $120.40   $120.40   $120.40  
  7 purchase totals = $712.66       $776.4521   $776.46   $776.50   $776.60