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 $182.92   10.592%   $202.2949   $202.29   $202.30   $202.30  
  Purchase #2 $134.59   13.355%   $152.5645   $152.56   $152.55   $152.60  
  Purchase #3 $80.48   6.313%   $85.5607   $85.56   $85.55   $85.60  
  Purchase #4 $23.93   12.327%   $26.8799   $26.88   $26.90   $26.90  
  Purchase #5 $201.25   4.811%   $210.9321   $210.93   $210.95   $210.90  
  Purchase #6 $49.50   7.333%   $53.1298   $53.13   $53.15   $53.10  
  Purchase #7 $119.52   11.851%   $133.6843   $133.68   $133.70   $133.70  
  7 purchase totals = $792.19       $865.0462   $865.03   $865.10   $865.10