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 $69.41   11.686%   $77.5213   $77.52   $77.50   $77.50  
  Purchase #2 $206.54   4.198%   $215.2105   $215.21   $215.20   $215.20  
  Purchase #3 $45.54   10.865%   $50.4879   $50.49   $50.50   $50.50  
  Purchase #4 $201.95   4.582%   $211.2033   $211.20   $211.20   $211.20  
  Purchase #5 $28.33   3.471%   $29.3133   $29.31   $29.30   $29.30  
  Purchase #6 $8.60   11.522%   $9.5909   $9.59   $9.60   $9.60  
  Purchase #7 $144.36   7.686%   $155.4555   $155.46   $155.45   $155.50  
  7 purchase totals = $704.73       $748.7827   $748.78   $748.75   $748.80