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 $105.40   3.772%   $109.3757   $109.38   $109.40   $109.40  
  Purchase #2 $187.70   11.418%   $209.1316   $209.13   $209.15   $209.10  
  Purchase #3 $144.41   11.483%   $160.9926   $160.99   $161.00   $161.00  
  Purchase #4 $75.51   6.854%   $80.6855   $80.69   $80.70   $80.70  
  Purchase #5 $195.51   13.527%   $221.9566   $221.96   $221.95   $222.00  
  Purchase #6 $89.53   13.709%   $101.8037   $101.80   $101.80   $101.80  
  Purchase #7 $112.85   11.359%   $125.6686   $125.67   $125.65   $125.70  
  7 purchase totals = $910.91       $1,009.6143   $1,009.62   $1,009.65   $1,009.70