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 $109.61   9.201%   $119.6952   $119.70   $119.70   $119.70  
  Purchase #2 $58.79   7.238%   $63.0452   $63.05   $63.05   $63.00  
  Purchase #3 $11.85   10.217%   $13.0607   $13.06   $13.05   $13.10  
  Purchase #4 $22.72   8.155%   $24.5728   $24.57   $24.55   $24.60  
  Purchase #5 $213.29   4.176%   $222.197   $222.20   $222.20   $222.20  
  Purchase #6 $9.78   6.831%   $10.4481   $10.45   $10.45   $10.40  
  Purchase #7 $146.31   4.784%   $153.3095   $153.31   $153.30   $153.30  
  7 purchase totals = $572.35       $606.3285   $606.34   $606.30   $606.30