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 $186.61   12.558%   $210.0445   $210.04   $210.05   $210.00  
  Purchase #2 $151.39   13.332%   $171.5733   $171.57   $171.55   $171.60  
  Purchase #3 $92.36   4.484%   $96.5014   $96.50   $96.50   $96.50  
  Purchase #4 $213.59   11.611%   $238.3899   $238.39   $238.40   $238.40  
  Purchase #5 $187.57   5.454%   $197.8001   $197.80   $197.80   $197.80  
  Purchase #6 $49.27   8.549%   $53.4821   $53.48   $53.50   $53.50  
  Purchase #7 $229.43   6.527%   $244.4049   $244.40   $244.40   $244.40  
  7 purchase totals = $1,110.22       $1,212.1962   $1,212.18   $1,212.20   $1,212.20