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 $233.98   6.496%   $249.1793   $249.18   $249.20   $249.20  
  Purchase #2 $195.39   3.860%   $202.9321   $202.93   $202.95   $202.90  
  Purchase #3 $122.91   8.598%   $133.4778   $133.48   $133.50   $133.50  
  Purchase #4 $67.97   5.118%   $71.4487   $71.45   $71.45   $71.40  
  Purchase #5 $246.28   12.781%   $277.757   $277.76   $277.75   $277.80  
  Purchase #6 $116.32   9.156%   $126.9703   $126.97   $126.95   $127.00  
  Purchase #7 $118.37   11.321%   $131.7707   $131.77   $131.75   $131.80  
  7 purchase totals = $1,101.22       $1,193.5359   $1,193.54   $1,193.55   $1,193.60