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 $183.96   10.687%   $203.6198   $203.62   $203.60   $203.60  
  Purchase #2 $124.92   6.160%   $132.6151   $132.62   $132.60   $132.60  
  Purchase #3 $242.69   9.596%   $265.9785   $265.98   $266.00   $266.00  
  Purchase #4 $220.98   10.801%   $244.848   $244.85   $244.85   $244.80  
  Purchase #5 $213.87   6.855%   $228.5308   $228.53   $228.55   $228.50  
  Purchase #6 $69.38   3.802%   $72.0178   $72.02   $72.00   $72.00  
  Purchase #7 $55.58   6.295%   $59.0788   $59.08   $59.10   $59.10  
  7 purchase totals = $1,111.38       $1,206.6888   $1,206.70   $1,206.70   $1,206.60