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 $65.77   6.102%   $69.7833   $69.78   $69.80   $69.80  
  Purchase #2 $172.93   10.728%   $191.4819   $191.48   $191.50   $191.50  
  Purchase #3 $161.60   11.240%   $179.7638   $179.76   $179.75   $179.80  
  Purchase #4 $179.87   4.424%   $187.8274   $187.83   $187.85   $187.80  
  Purchase #5 $139.86   5.798%   $147.9691   $147.97   $147.95   $148.00  
  Purchase #6 $93.92   11.121%   $104.3648   $104.36   $104.35   $104.40  
  Purchase #7 $127.79   4.131%   $133.069   $133.07   $133.05   $133.10  
  7 purchase totals = $941.74       $1,014.2593   $1,014.25   $1,014.25   $1,014.40