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 $214.51   9.364%   $234.5967   $234.60   $234.60   $234.60  
  Purchase #2 $237.54   12.728%   $267.7741   $267.77   $267.75   $267.80  
  Purchase #3 $83.94   4.346%   $87.588   $87.59   $87.60   $87.60  
  Purchase #4 $237.35   5.489%   $250.3781   $250.38   $250.40   $250.40  
  Purchase #5 $179.94   8.362%   $194.9866   $194.99   $195.00   $195.00  
  Purchase #6 $84.63   5.372%   $89.1763   $89.18   $89.20   $89.20  
  Purchase #7 $31.82   8.867%   $34.6415   $34.64   $34.65   $34.60  
  7 purchase totals = $1,069.73       $1,159.1413   $1,159.15   $1,159.20   $1,159.20