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 $57.79   4.852%   $60.594   $60.59   $60.60   $60.60  
  Purchase #2 $239.45   11.816%   $267.7434   $267.74   $267.75   $267.70  
  Purchase #3 $195.29   7.407%   $209.7551   $209.76   $209.75   $209.80  
  Purchase #4 $101.25   7.539%   $108.8832   $108.88   $108.90   $108.90  
  Purchase #5 $84.86   5.545%   $89.5655   $89.57   $89.55   $89.60  
  Purchase #6 $215.38   7.551%   $231.6433   $231.64   $231.65   $231.60  
  Purchase #7 $212.90   4.789%   $223.0958   $223.10   $223.10   $223.10  
  7 purchase totals = $1,106.92       $1,191.2803   $1,191.28   $1,191.30   $1,191.30