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 $131.71   13.121%   $148.9917   $148.99   $149.00   $149.00  
  Purchase #2 $194.85   10.185%   $214.6955   $214.70   $214.70   $214.70  
  Purchase #3 $181.51   10.286%   $200.1801   $200.18   $200.20   $200.20  
  Purchase #4 $237.98   3.826%   $247.0851   $247.09   $247.10   $247.10  
  Purchase #5 $162.68   6.423%   $173.1289   $173.13   $173.15   $173.10  
  Purchase #6 $207.49   13.351%   $235.192   $235.19   $235.20   $235.20  
  Purchase #7 $95.84   13.222%   $108.512   $108.51   $108.50   $108.50  
  7 purchase totals = $1,212.06       $1,327.7853   $1,327.79   $1,327.85   $1,327.80