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 $85.84   12.813%   $96.8387   $96.84   $96.85   $96.80  
  Purchase #2 $95.77   11.321%   $106.6121   $106.61   $106.60   $106.60  
  Purchase #3 $226.75   4.848%   $237.7428   $237.74   $237.75   $237.70  
  Purchase #4 $141.40   13.161%   $160.0097   $160.01   $160.00   $160.00  
  Purchase #5 $153.68   9.808%   $168.7529   $168.75   $168.75   $168.80  
  Purchase #6 $133.74   6.397%   $142.2953   $142.30   $142.30   $142.30  
  Purchase #7 $32.87   3.612%   $34.0573   $34.06   $34.05   $34.10  
  7 purchase totals = $870.05       $946.3088   $946.31   $946.30   $946.30