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 $116.98   10.506%   $129.2699   $129.27   $129.25   $129.30  
  Purchase #2 $171.68   11.680%   $191.7322   $191.73   $191.75   $191.70  
  Purchase #3 $208.66   4.264%   $217.5573   $217.56   $217.55   $217.60  
  Purchase #4 $64.82   10.326%   $71.5133   $71.51   $71.50   $71.50  
  Purchase #5 $151.74   6.644%   $161.8216   $161.82   $161.80   $161.80  
  Purchase #6 $105.91   12.184%   $118.8141   $118.81   $118.80   $118.80  
  Purchase #7 $155.48   7.397%   $166.9809   $166.98   $167.00   $167.00  
  7 purchase totals = $975.27       $1,057.6893   $1,057.68   $1,057.65   $1,057.70