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 $182.41   10.730%   $201.9826   $201.98   $202.00   $202.00  
  Purchase #2 $226.75   5.691%   $239.6543   $239.65   $239.65   $239.70  
  Purchase #3 $167.31   8.104%   $180.8688   $180.87   $180.85   $180.90  
  Purchase #4 $196.42   10.234%   $216.5216   $216.52   $216.50   $216.50  
  Purchase #5 $42.36   12.512%   $47.6601   $47.66   $47.65   $47.70  
  Purchase #6 $235.96   11.315%   $262.6589   $262.66   $262.65   $262.70  
  Purchase #7 $113.90   13.682%   $129.4838   $129.48   $129.50   $129.50  
  7 purchase totals = $1,165.11       $1,278.8301   $1,278.82   $1,278.80   $1,279.00