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 $248.54   6.442%   $264.5509   $264.55   $264.55   $264.60  
  Purchase #2 $9.60   6.624%   $10.2359   $10.24   $10.25   $10.20  
  Purchase #3 $123.77   12.146%   $138.8031   $138.80   $138.80   $138.80  
  Purchase #4 $27.53   6.479%   $29.3137   $29.31   $29.30   $29.30  
  Purchase #5 $215.94   6.126%   $229.1685   $229.17   $229.15   $229.20  
  Purchase #6 $69.68   8.673%   $75.7233   $75.72   $75.70   $75.70  
  Purchase #7 $244.86   8.755%   $266.2975   $266.30   $266.30   $266.30  
  7 purchase totals = $939.92       $1,014.0929   $1,014.09   $1,014.05   $1,014.10