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 $103.75   11.762%   $115.9531   $115.95   $115.95   $116.00  
  Purchase #2 $156.41   5.495%   $165.0047   $165.00   $165.00   $165.00  
  Purchase #3 $85.77   10.375%   $94.6686   $94.67   $94.65   $94.70  
  Purchase #4 $93.44   4.115%   $97.2851   $97.29   $97.30   $97.30  
  Purchase #5 $193.57   13.355%   $219.4213   $219.42   $219.40   $219.40  
  Purchase #6 $185.81   9.190%   $202.8859   $202.89   $202.90   $202.90  
  Purchase #7 $126.31   4.659%   $132.1948   $132.19   $132.20   $132.20  
  7 purchase totals = $945.06       $1,027.4135   $1,027.41   $1,027.40   $1,027.50