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 $23.66   5.753%   $25.0212   $25.02   $25.00   $25.00  
  Purchase #2 $44.96   6.284%   $47.7853   $47.79   $47.80   $47.80  
  Purchase #3 $205.50   3.509%   $212.711   $212.71   $212.70   $212.70  
  Purchase #4 $100.39   10.465%   $110.8958   $110.90   $110.90   $110.90  
  Purchase #5 $162.67   3.236%   $167.934   $167.93   $167.95   $167.90  
  Purchase #6 $85.88   8.409%   $93.1016   $93.10   $93.10   $93.10  
  Purchase #7 $217.68   3.137%   $224.5086   $224.51   $224.50   $224.50  
  7 purchase totals = $840.74       $881.9575   $881.96   $881.95   $881.90