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 $229.98   7.844%   $248.0196   $248.02   $248.00   $248.00  
  Purchase #2 $88.82   9.611%   $97.3565   $97.36   $97.35   $97.40  
  Purchase #3 $32.89   9.255%   $35.934   $35.93   $35.95   $35.90  
  Purchase #4 $248.26   5.728%   $262.4803   $262.48   $262.50   $262.50  
  Purchase #5 $39.47   7.456%   $42.4129   $42.41   $42.40   $42.40  
  Purchase #6 $234.47   8.582%   $254.5922   $254.59   $254.60   $254.60  
  Purchase #7 $54.79   5.712%   $57.9196   $57.92   $57.90   $57.90  
  7 purchase totals = $928.68       $998.7151   $998.71   $998.70   $998.70