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 $225.51   5.183%   $237.1982   $237.20   $237.20   $237.20  
  Purchase #2 $61.28   5.840%   $64.8588   $64.86   $64.85   $64.90  
  Purchase #3 $118.85   5.612%   $125.5199   $125.52   $125.50   $125.50  
  Purchase #4 $167.31   9.383%   $183.0087   $183.01   $183.00   $183.00  
  Purchase #5 $188.27   13.714%   $214.0893   $214.09   $214.10   $214.10  
  Purchase #6 $108.80   6.242%   $115.5913   $115.59   $115.60   $115.60  
  Purchase #7 $87.98   10.452%   $97.1757   $97.18   $97.20   $97.20  
  7 purchase totals = $958.00       $1,037.4419   $1,037.45   $1,037.45   $1,037.50