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 $136.92   10.498%   $151.2939   $151.29   $151.30   $151.30  
  Purchase #2 $34.28   3.462%   $35.4668   $35.47   $35.45   $35.50  
  Purchase #3 $197.50   10.368%   $217.9768   $217.98   $218.00   $218.00  
  Purchase #4 $249.75   8.711%   $271.5057   $271.51   $271.50   $271.50  
  Purchase #5 $231.44   13.728%   $263.2121   $263.21   $263.20   $263.20  
  Purchase #6 $167.96   9.671%   $184.2034   $184.20   $184.20   $184.20  
  Purchase #7 $210.40   9.692%   $230.792   $230.79   $230.80   $230.80  
  7 purchase totals = $1,228.25       $1,354.4507   $1,354.45   $1,354.45   $1,354.50