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 $87.94   6.507%   $93.6623   $93.66   $93.65   $93.70  
  Purchase #2 $224.44   3.328%   $231.9094   $231.91   $231.90   $231.90  
  Purchase #3 $47.74   6.739%   $50.9572   $50.96   $50.95   $51.00  
  Purchase #4 $162.43   8.181%   $175.7184   $175.72   $175.70   $175.70  
  Purchase #5 $153.79   8.789%   $167.3066   $167.31   $167.30   $167.30  
  Purchase #6 $69.29   12.445%   $77.9131   $77.91   $77.90   $77.90  
  Purchase #7 $15.59   11.140%   $17.3267   $17.33   $17.35   $17.30  
  7 purchase totals = $761.22       $814.7937   $814.80   $814.75   $814.80