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 $232.35   5.331%   $244.7366   $244.74   $244.75   $244.70  
  Purchase #2 $33.39   4.743%   $34.9737   $34.97   $34.95   $35.00  
  Purchase #3 $10.58   9.116%   $11.5445   $11.54   $11.55   $11.50  
  Purchase #4 $241.88   7.805%   $260.7587   $260.76   $260.75   $260.80  
  Purchase #5 $110.63   11.375%   $123.2142   $123.21   $123.20   $123.20  
  Purchase #6 $199.45   8.647%   $216.6964   $216.70   $216.70   $216.70  
  Purchase #7 $124.65   6.667%   $132.9604   $132.96   $132.95   $133.00  
  7 purchase totals = $952.93       $1,024.8845   $1,024.88   $1,024.85   $1,024.90