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 $183.31   5.648%   $193.6633   $193.66   $193.65   $193.70  
  Purchase #2 $26.89   3.844%   $27.9237   $27.92   $27.90   $27.90  
  Purchase #3 $211.70   5.355%   $223.0365   $223.04   $223.05   $223.00  
  Purchase #4 $27.67   7.133%   $29.6437   $29.64   $29.65   $29.60  
  Purchase #5 $89.67   4.181%   $93.4191   $93.42   $93.40   $93.40  
  Purchase #6 $247.59   8.499%   $268.6327   $268.63   $268.65   $268.60  
  Purchase #7 $61.36   5.677%   $64.8434   $64.84   $64.85   $64.80  
  7 purchase totals = $848.19       $901.1624   $901.15   $901.15   $901.00