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 $233.48   8.477%   $253.2721   $253.27   $253.25   $253.30  
  Purchase #2 $237.82   12.327%   $267.1361   $267.14   $267.15   $267.10  
  Purchase #3 $172.74   8.760%   $187.872   $187.87   $187.85   $187.90  
  Purchase #4 $68.52   9.736%   $75.1911   $75.19   $75.20   $75.20  
  Purchase #5 $8.30   12.517%   $9.3389   $9.34   $9.35   $9.30  
  Purchase #6 $189.72   8.852%   $206.514   $206.51   $206.50   $206.50  
  Purchase #7 $32.76   6.837%   $34.9998   $35.00   $35.00   $35.00  
  7 purchase totals = $943.34       $1,034.3240   $1,034.32   $1,034.30   $1,034.30