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 $92.66   8.575%   $100.6056   $100.61   $100.60   $100.60  
  Purchase #2 $119.34   10.580%   $131.9662   $131.97   $131.95   $132.00  
  Purchase #3 $175.54   3.475%   $181.64   $181.64   $181.65   $181.60  
  Purchase #4 $94.62   8.503%   $102.6655   $102.67   $102.65   $102.70  
  Purchase #5 $199.57   4.284%   $208.1196   $208.12   $208.10   $208.10  
  Purchase #6 $209.46   11.372%   $233.2798   $233.28   $233.30   $233.30  
  Purchase #7 $58.29   8.190%   $63.064   $63.06   $63.05   $63.10  
  7 purchase totals = $949.48       $1,021.3407   $1,021.35   $1,021.30   $1,021.40