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 $31.82   5.867%   $33.6869   $33.69   $33.70   $33.70  
  Purchase #2 $224.45   11.251%   $249.7029   $249.70   $249.70   $249.70  
  Purchase #3 $151.29   12.437%   $170.1059   $170.11   $170.10   $170.10  
  Purchase #4 $119.71   4.209%   $124.7486   $124.75   $124.75   $124.70  
  Purchase #5 $239.49   11.503%   $267.0385   $267.04   $267.05   $267.00  
  Purchase #6 $168.58   6.192%   $179.0185   $179.02   $179.00   $179.00  
  Purchase #7 $67.35   6.859%   $71.9695   $71.97   $71.95   $72.00  
  7 purchase totals = $1,002.69       $1,096.2708   $1,096.28   $1,096.25   $1,096.20