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 $217.25   8.256%   $235.1862   $235.19   $235.20   $235.20  
  Purchase #2 $244.43   3.227%   $252.3178   $252.32   $252.30   $252.30  
  Purchase #3 $221.64   4.218%   $230.9888   $230.99   $231.00   $231.00  
  Purchase #4 $129.27   4.424%   $134.9889   $134.99   $135.00   $135.00  
  Purchase #5 $209.30   4.300%   $218.2999   $218.30   $218.30   $218.30  
  Purchase #6 $187.71   4.114%   $195.4324   $195.43   $195.45   $195.40  
  Purchase #7 $77.68   12.793%   $87.6176   $87.62   $87.60   $87.60  
  7 purchase totals = $1,287.28       $1,354.8316   $1,354.84   $1,354.85   $1,354.80