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 $53.96   9.462%   $59.0657   $59.07   $59.05   $59.10  
  Purchase #2 $17.30   3.122%   $17.8401   $17.84   $17.85   $17.80  
  Purchase #3 $109.65   10.411%   $121.0657   $121.07   $121.05   $121.10  
  Purchase #4 $112.77   13.804%   $128.3368   $128.34   $128.35   $128.30  
  Purchase #5 $233.72   13.817%   $266.0131   $266.01   $266.00   $266.00  
  Purchase #6 $244.29   7.339%   $262.2184   $262.22   $262.20   $262.20  
  Purchase #7 $134.99   9.212%   $147.4253   $147.43   $147.45   $147.40  
  7 purchase totals = $906.68       $1,001.9651   $1,001.98   $1,001.95   $1,001.90