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 $62.73   12.257%   $70.4188   $70.42   $70.40   $70.40  
  Purchase #2 $152.36   6.708%   $162.5803   $162.58   $162.60   $162.60  
  Purchase #3 $61.74   12.460%   $69.4328   $69.43   $69.45   $69.40  
  Purchase #4 $241.91   8.566%   $262.632   $262.63   $262.65   $262.60  
  Purchase #5 $239.29   11.672%   $267.2199   $267.22   $267.20   $267.20  
  Purchase #6 $143.75   10.651%   $159.0608   $159.06   $159.05   $159.10  
  Purchase #7 $30.33   9.430%   $33.1901   $33.19   $33.20   $33.20  
  7 purchase totals = $932.11       $1,024.5347   $1,024.53   $1,024.55   $1,024.50