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 $204.71   13.287%   $231.9098   $231.91   $231.90   $231.90  
  Purchase #2 $157.81   4.825%   $165.4243   $165.42   $165.40   $165.40  
  Purchase #3 $46.98   6.615%   $50.0877   $50.09   $50.10   $50.10  
  Purchase #4 $66.37   13.269%   $75.1766   $75.18   $75.20   $75.20  
  Purchase #5 $72.58   8.215%   $78.5424   $78.54   $78.55   $78.50  
  Purchase #6 $182.38   13.539%   $207.0724   $207.07   $207.05   $207.10  
  Purchase #7 $219.35   4.327%   $228.8413   $228.84   $228.85   $228.80  
  7 purchase totals = $950.18       $1,037.0545   $1,037.05   $1,037.05   $1,037.00