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 $247.92   11.754%   $277.0605   $277.06   $277.05   $277.10  
  Purchase #2 $53.92   8.506%   $58.5064   $58.51   $58.50   $58.50  
  Purchase #3 $221.70   3.212%   $228.821   $228.82   $228.80   $228.80  
  Purchase #4 $101.65   4.501%   $106.2253   $106.23   $106.25   $106.20  
  Purchase #5 $146.51   8.732%   $159.3033   $159.30   $159.30   $159.30  
  Purchase #6 $25.27   3.278%   $26.0984   $26.10   $26.10   $26.10  
  Purchase #7 $199.90   5.291%   $210.4767   $210.48   $210.50   $210.50  
  7 purchase totals = $996.87       $1,066.4916   $1,066.50   $1,066.50   $1,066.50