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 $147.75   12.761%   $166.6044   $166.60   $166.60   $166.60  
  Purchase #2 $119.91   13.813%   $136.4732   $136.47   $136.45   $136.50  
  Purchase #3 $98.97   4.409%   $103.3336   $103.33   $103.35   $103.30  
  Purchase #4 $24.58   9.588%   $26.9367   $26.94   $26.95   $26.90  
  Purchase #5 $135.82   11.326%   $151.203   $151.20   $151.20   $151.20  
  Purchase #6 $116.55   10.624%   $128.9323   $128.93   $128.95   $128.90  
  Purchase #7 $54.62   7.692%   $58.8214   $58.82   $58.80   $58.80  
  7 purchase totals = $698.20       $772.3046   $772.29   $772.30   $772.20