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 $232.87   11.821%   $260.3976   $260.40   $260.40   $260.40  
  Purchase #2 $203.94   4.767%   $213.6618   $213.66   $213.65   $213.70  
  Purchase #3 $116.46   13.771%   $132.4977   $132.50   $132.50   $132.50  
  Purchase #4 $22.81   6.766%   $24.3533   $24.35   $24.35   $24.40  
  Purchase #5 $99.50   9.552%   $109.0042   $109.00   $109.00   $109.00  
  Purchase #6 $246.57   10.563%   $272.6152   $272.62   $272.60   $272.60  
  Purchase #7 $194.36   8.168%   $210.2353   $210.24   $210.25   $210.20  
  7 purchase totals = $1,116.51       $1,222.7651   $1,222.77   $1,222.75   $1,222.80