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 $182.95   10.809%   $202.7251   $202.73   $202.75   $202.70  
  Purchase #2 $123.60   4.112%   $128.6824   $128.68   $128.70   $128.70  
  Purchase #3 $166.79   7.569%   $179.4143   $179.41   $179.40   $179.40  
  Purchase #4 $24.84   5.420%   $26.1863   $26.19   $26.20   $26.20  
  Purchase #5 $133.82   13.563%   $151.97   $151.97   $151.95   $152.00  
  Purchase #6 $159.46   11.136%   $177.2175   $177.22   $177.20   $177.20  
  Purchase #7 $119.83   6.390%   $127.4871   $127.49   $127.50   $127.50  
  7 purchase totals = $911.29       $993.6827   $993.69   $993.70   $993.70