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 $240.94   11.158%   $267.8241   $267.82   $267.80   $267.80  
  Purchase #2 $194.55   3.774%   $201.8923   $201.89   $201.90   $201.90  
  Purchase #3 $171.82   4.222%   $179.0742   $179.07   $179.05   $179.10  
  Purchase #4 $46.81   8.339%   $50.7135   $50.71   $50.70   $50.70  
  Purchase #5 $23.90   3.150%   $24.6529   $24.65   $24.65   $24.70  
  Purchase #6 $22.87   7.833%   $24.6614   $24.66   $24.65   $24.70  
  Purchase #7 $17.51   8.327%   $18.9681   $18.97   $18.95   $19.00  
  7 purchase totals = $718.40       $767.7865   $767.77   $767.70   $767.90