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 $242.43   12.761%   $273.3665   $273.37   $273.35   $273.40  
  Purchase #2 $90.35   6.821%   $96.5128   $96.51   $96.50   $96.50  
  Purchase #3 $222.53   6.356%   $236.674   $236.67   $236.65   $236.70  
  Purchase #4 $134.30   13.409%   $152.3083   $152.31   $152.30   $152.30  
  Purchase #5 $55.84   4.592%   $58.4042   $58.40   $58.40   $58.40  
  Purchase #6 $135.98   7.610%   $146.3281   $146.33   $146.35   $146.30  
  Purchase #7 $84.38   4.274%   $87.9864   $87.99   $88.00   $88.00  
  7 purchase totals = $965.81       $1,051.5803   $1,051.58   $1,051.55   $1,051.60