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 $142.53   13.871%   $162.3003   $162.30   $162.30   $162.30  
  Purchase #2 $245.98   5.223%   $258.8275   $258.83   $258.85   $258.80  
  Purchase #3 $148.37   4.731%   $155.3894   $155.39   $155.40   $155.40  
  Purchase #4 $171.77   3.836%   $178.3591   $178.36   $178.35   $178.40  
  Purchase #5 $67.69   11.733%   $75.6321   $75.63   $75.65   $75.60  
  Purchase #6 $69.97   5.226%   $73.6266   $73.63   $73.65   $73.60  
  Purchase #7 $134.27   8.798%   $146.0831   $146.08   $146.10   $146.10  
  7 purchase totals = $980.58       $1,050.2181   $1,050.22   $1,050.30   $1,050.20