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 $228.76   7.554%   $246.0405   $246.04   $246.05   $246.00  
  Purchase #2 $216.70   5.578%   $228.7875   $228.79   $228.80   $228.80  
  Purchase #3 $89.62   9.680%   $98.2952   $98.30   $98.30   $98.30  
  Purchase #4 $143.97   6.642%   $153.5325   $153.53   $153.55   $153.50  
  Purchase #5 $165.91   12.116%   $186.0117   $186.01   $186.00   $186.00  
  Purchase #6 $193.48   12.313%   $217.3032   $217.30   $217.30   $217.30  
  Purchase #7 $36.61   9.845%   $40.2143   $40.21   $40.20   $40.20  
  7 purchase totals = $1,075.05       $1,170.1849   $1,170.18   $1,170.20   $1,170.10