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 $197.82   8.528%   $214.6901   $214.69   $214.70   $214.70  
  Purchase #2 $53.64   8.554%   $58.2284   $58.23   $58.25   $58.20  
  Purchase #3 $194.25   9.402%   $212.5134   $212.51   $212.50   $212.50  
  Purchase #4 $129.33   11.277%   $143.9145   $143.91   $143.90   $143.90  
  Purchase #5 $231.76   9.449%   $253.659   $253.66   $253.65   $253.70  
  Purchase #6 $39.34   12.544%   $44.2748   $44.27   $44.25   $44.30  
  Purchase #7 $154.93   5.551%   $163.5302   $163.53   $163.55   $163.50  
  7 purchase totals = $1,001.07       $1,090.8104   $1,090.80   $1,090.80   $1,090.80