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 $51.74   5.777%   $54.729   $54.73   $54.75   $54.70  
  Purchase #2 $218.52   5.697%   $230.9691   $230.97   $230.95   $231.00  
  Purchase #3 $61.45   13.321%   $69.6358   $69.64   $69.65   $69.60  
  Purchase #4 $165.31   11.243%   $183.8958   $183.90   $183.90   $183.90  
  Purchase #5 $156.98   11.311%   $174.736   $174.74   $174.75   $174.70  
  Purchase #6 $204.54   4.281%   $213.2964   $213.30   $213.30   $213.30  
  Purchase #7 $140.85   12.695%   $158.7309   $158.73   $158.75   $158.70  
  7 purchase totals = $999.39       $1,085.9930   $1,086.01   $1,086.05   $1,085.90