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 $58.26   4.596%   $60.9376   $60.94   $60.95   $60.90  
  Purchase #2 $99.39   5.569%   $104.925   $104.93   $104.95   $104.90  
  Purchase #3 $30.28   7.461%   $32.5392   $32.54   $32.55   $32.50  
  Purchase #4 $202.57   12.172%   $227.2268   $227.23   $227.25   $227.20  
  Purchase #5 $102.44   12.294%   $115.034   $115.03   $115.05   $115.00  
  Purchase #6 $29.79   6.167%   $31.6271   $31.63   $31.65   $31.60  
  Purchase #7 $110.38   12.761%   $124.4656   $124.47   $124.45   $124.50  
  7 purchase totals = $633.11       $696.7553   $696.77   $696.85   $696.60