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 $44.66   11.863%   $49.958   $49.96   $49.95   $50.00  
  Purchase #2 $25.53   5.596%   $26.9587   $26.96   $26.95   $27.00  
  Purchase #3 $185.29   7.867%   $199.8668   $199.87   $199.85   $199.90  
  Purchase #4 $208.31   7.737%   $224.4269   $224.43   $224.45   $224.40  
  Purchase #5 $137.88   6.792%   $147.2448   $147.24   $147.25   $147.20  
  Purchase #6 $110.39   9.433%   $120.8031   $120.80   $120.80   $120.80  
  Purchase #7 $236.55   8.552%   $256.7798   $256.78   $256.80   $256.80  
  7 purchase totals = $948.61       $1,026.0381   $1,026.04   $1,026.05   $1,026.10