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 $119.74   12.495%   $134.7015   $134.70   $134.70   $134.70  
  Purchase #2 $213.34   11.861%   $238.6443   $238.64   $238.65   $238.60  
  Purchase #3 $15.29   6.216%   $16.2404   $16.24   $16.25   $16.20  
  Purchase #4 $138.45   8.584%   $150.3345   $150.33   $150.35   $150.30  
  Purchase #5 $228.94   3.186%   $236.234   $236.23   $236.25   $236.20  
  Purchase #6 $228.59   11.566%   $255.0287   $255.03   $255.05   $255.00  
  Purchase #7 $11.59   6.426%   $12.3348   $12.33   $12.35   $12.30  
  7 purchase totals = $955.94       $1,043.5182   $1,043.50   $1,043.60   $1,043.30