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 $59.88   12.839%   $67.568   $67.57   $67.55   $67.60  
  Purchase #2 $68.48   13.624%   $77.8097   $77.81   $77.80   $77.80  
  Purchase #3 $219.69   9.738%   $241.0834   $241.08   $241.10   $241.10  
  Purchase #4 $16.98   3.252%   $17.5322   $17.53   $17.55   $17.50  
  Purchase #5 $211.80   3.822%   $219.895   $219.90   $219.90   $219.90  
  Purchase #6 $222.42   5.300%   $234.2083   $234.21   $234.20   $234.20  
  Purchase #7 $135.29   7.276%   $145.1337   $145.13   $145.15   $145.10  
  7 purchase totals = $934.54       $1,003.2303   $1,003.23   $1,003.25   $1,003.20