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 $154.47   9.311%   $168.8527   $168.85   $168.85   $168.90  
  Purchase #2 $165.73   4.200%   $172.6907   $172.69   $172.70   $172.70  
  Purchase #3 $23.70   5.532%   $25.0111   $25.01   $25.00   $25.00  
  Purchase #4 $92.56   12.453%   $104.0865   $104.09   $104.10   $104.10  
  Purchase #5 $68.28   6.365%   $72.626   $72.63   $72.65   $72.60  
  Purchase #6 $220.95   10.778%   $244.764   $244.76   $244.75   $244.80  
  Purchase #7 $221.69   4.776%   $232.2779   $232.28   $232.30   $232.30  
  7 purchase totals = $947.38       $1,020.3089   $1,020.31   $1,020.35   $1,020.40