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 $232.69   13.264%   $263.554   $263.55   $263.55   $263.60  
  Purchase #2 $113.30   9.656%   $124.2402   $124.24   $124.25   $124.20  
  Purchase #3 $91.33   4.669%   $95.5942   $95.59   $95.60   $95.60  
  Purchase #4 $241.28   11.120%   $268.1103   $268.11   $268.10   $268.10  
  Purchase #5 $75.28   6.170%   $79.9248   $79.92   $79.90   $79.90  
  Purchase #6 $147.87   11.341%   $164.6399   $164.64   $164.65   $164.60  
  Purchase #7 $221.59   7.477%   $238.1583   $238.16   $238.15   $238.20  
  7 purchase totals = $1,123.34       $1,234.2217   $1,234.21   $1,234.20   $1,234.20