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 $55.32   9.772%   $60.7259   $60.73   $60.75   $60.70  
  Purchase #2 $54.37   12.862%   $61.3631   $61.36   $61.35   $61.40  
  Purchase #3 $115.70   6.659%   $123.4045   $123.40   $123.40   $123.40  
  Purchase #4 $246.77   11.847%   $276.0048   $276.00   $276.00   $276.00  
  Purchase #5 $159.86   6.764%   $170.6729   $170.67   $170.65   $170.70  
  Purchase #6 $62.65   12.546%   $70.5101   $70.51   $70.50   $70.50  
  Purchase #7 $246.95   6.439%   $262.8511   $262.85   $262.85   $262.90  
  7 purchase totals = $941.62       $1,025.5324   $1,025.52   $1,025.50   $1,025.60