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 $58.72   9.482%   $64.2878   $64.29   $64.30   $64.30  
  Purchase #2 $192.79   11.783%   $215.5064   $215.51   $215.50   $215.50  
  Purchase #3 $78.52   7.371%   $84.3077   $84.31   $84.30   $84.30  
  Purchase #4 $85.61   7.388%   $91.9349   $91.93   $91.95   $91.90  
  Purchase #5 $115.97   9.599%   $127.102   $127.10   $127.10   $127.10  
  Purchase #6 $66.39   5.496%   $70.0388   $70.04   $70.05   $70.00  
  Purchase #7 $95.27   7.827%   $102.7268   $102.73   $102.75   $102.70  
  7 purchase totals = $693.27       $755.9044   $755.91   $755.95   $755.80