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 $61.87   6.645%   $65.9813   $65.98   $66.00   $66.00  
  Purchase #2 $103.49   9.208%   $113.0194   $113.02   $113.00   $113.00  
  Purchase #3 $152.86   9.487%   $167.3618   $167.36   $167.35   $167.40  
  Purchase #4 $231.97   3.210%   $239.4162   $239.42   $239.40   $239.40  
  Purchase #5 $219.79   12.393%   $247.0286   $247.03   $247.05   $247.00  
  Purchase #6 $10.89   3.357%   $11.2556   $11.26   $11.25   $11.30  
  Purchase #7 $186.56   8.427%   $202.2814   $202.28   $202.30   $202.30  
  7 purchase totals = $967.43       $1,046.3443   $1,046.35   $1,046.35   $1,046.40