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 $174.32   7.622%   $187.6067   $187.61   $187.60   $187.60  
  Purchase #2 $228.32   11.338%   $254.2069   $254.21   $254.20   $254.20  
  Purchase #3 $75.47   10.324%   $83.2615   $83.26   $83.25   $83.30  
  Purchase #4 $161.60   12.787%   $182.2638   $182.26   $182.25   $182.30  
  Purchase #5 $188.95   7.398%   $202.9285   $202.93   $202.95   $202.90  
  Purchase #6 $119.32   3.236%   $123.1812   $123.18   $123.20   $123.20  
  Purchase #7 $27.79   13.535%   $31.5514   $31.55   $31.55   $31.60  
  7 purchase totals = $975.77       $1,065.0000   $1,065.00   $1,065.00   $1,065.10