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 $223.68   7.728%   $240.966   $240.97   $240.95   $241.00  
  Purchase #2 $142.49   10.653%   $157.6695   $157.67   $157.65   $157.70  
  Purchase #3 $203.38   12.348%   $228.4934   $228.49   $228.50   $228.50  
  Purchase #4 $187.30   3.673%   $194.1795   $194.18   $194.20   $194.20  
  Purchase #5 $67.50   9.829%   $74.1346   $74.13   $74.15   $74.10  
  Purchase #6 $161.62   10.508%   $178.603   $178.60   $178.60   $178.60  
  Purchase #7 $95.66   6.232%   $101.6215   $101.62   $101.60   $101.60  
  7 purchase totals = $1,081.63       $1,175.6675   $1,175.66   $1,175.65   $1,175.70