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 $96.94   5.181%   $101.9625   $101.96   $101.95   $102.00  
  Purchase #2 $49.67   11.118%   $55.1923   $55.19   $55.20   $55.20  
  Purchase #3 $240.32   12.126%   $269.4612   $269.46   $269.45   $269.50  
  Purchase #4 $213.31   7.221%   $228.7131   $228.71   $228.70   $228.70  
  Purchase #5 $248.54   12.601%   $279.8585   $279.86   $279.85   $279.90  
  Purchase #6 $195.48   3.595%   $202.5075   $202.51   $202.50   $202.50  
  Purchase #7 $152.65   4.367%   $159.3162   $159.32   $159.30   $159.30  
  7 purchase totals = $1,196.91       $1,297.0113   $1,297.01   $1,296.95   $1,297.10