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 $105.81   10.786%   $117.2227   $117.22   $117.20   $117.20  
  Purchase #2 $148.68   4.119%   $154.8041   $154.80   $154.80   $154.80  
  Purchase #3 $61.32   8.255%   $66.382   $66.38   $66.40   $66.40  
  Purchase #4 $51.78   13.468%   $58.7537   $58.75   $58.75   $58.80  
  Purchase #5 $200.67   6.115%   $212.941   $212.94   $212.95   $212.90  
  Purchase #6 $198.90   5.669%   $210.1756   $210.18   $210.20   $210.20  
  Purchase #7 $23.36   7.220%   $25.0466   $25.05   $25.05   $25.00  
  7 purchase totals = $790.52       $845.3257   $845.32   $845.35   $845.30