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 $32.59   12.791%   $36.7586   $36.76   $36.75   $36.80  
  Purchase #2 $223.65   4.158%   $232.9494   $232.95   $232.95   $232.90  
  Purchase #3 $165.55   3.108%   $170.6953   $170.70   $170.70   $170.70  
  Purchase #4 $57.98   9.268%   $63.3536   $63.35   $63.35   $63.40  
  Purchase #5 $124.33   6.756%   $132.7297   $132.73   $132.75   $132.70  
  Purchase #6 $104.73   5.576%   $110.5697   $110.57   $110.55   $110.60  
  Purchase #7 $244.56   6.547%   $260.5713   $260.57   $260.55   $260.60  
  7 purchase totals = $953.39       $1,007.6276   $1,007.63   $1,007.60   $1,007.70