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 $53.64   9.254%   $58.6038   $58.60   $58.60   $58.60  
  Purchase #2 $203.92   5.825%   $215.7983   $215.80   $215.80   $215.80  
  Purchase #3 $219.65   8.195%   $237.6503   $237.65   $237.65   $237.70  
  Purchase #4 $64.58   8.559%   $70.1074   $70.11   $70.10   $70.10  
  Purchase #5 $223.92   10.568%   $247.5839   $247.58   $247.60   $247.60  
  Purchase #6 $151.56   6.767%   $161.8161   $161.82   $161.80   $161.80  
  Purchase #7 $75.76   4.431%   $79.1169   $79.12   $79.10   $79.10  
  7 purchase totals = $993.03       $1,070.6767   $1,070.68   $1,070.65   $1,070.70