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 $237.87   3.732%   $246.7473   $246.75   $246.75   $246.70  
  Purchase #2 $129.33   13.535%   $146.8348   $146.83   $146.85   $146.80  
  Purchase #3 $179.43   4.554%   $187.6012   $187.60   $187.60   $187.60  
  Purchase #4 $115.44   12.746%   $130.154   $130.15   $130.15   $130.20  
  Purchase #5 $203.26   11.662%   $226.9642   $226.96   $226.95   $227.00  
  Purchase #6 $24.56   11.256%   $27.3245   $27.32   $27.30   $27.30  
  Purchase #7 $176.55   10.227%   $194.6058   $194.61   $194.60   $194.60  
  7 purchase totals = $1,066.44       $1,160.2318   $1,160.22   $1,160.20   $1,160.20