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 $55.88   9.132%   $60.983   $60.98   $61.00   $61.00  
  Purchase #2 $25.38   8.661%   $27.5782   $27.58   $27.60   $27.60  
  Purchase #3 $59.82   10.606%   $66.1645   $66.16   $66.15   $66.20  
  Purchase #4 $161.72   13.590%   $183.6977   $183.70   $183.70   $183.70  
  Purchase #5 $240.86   6.115%   $255.5886   $255.59   $255.60   $255.60  
  Purchase #6 $26.70   8.173%   $28.8822   $28.88   $28.90   $28.90  
  Purchase #7 $128.76   4.554%   $134.6237   $134.62   $134.60   $134.60  
  7 purchase totals = $699.12       $757.5179   $757.51   $757.55   $757.60