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 $174.92   13.597%   $198.7039   $198.70   $198.70   $198.70  
  Purchase #2 $240.84   3.392%   $249.0093   $249.01   $249.00   $249.00  
  Purchase #3 $171.63   11.746%   $191.7897   $191.79   $191.80   $191.80  
  Purchase #4 $14.90   6.331%   $15.8433   $15.84   $15.85   $15.80  
  Purchase #5 $191.96   11.622%   $214.2696   $214.27   $214.25   $214.30  
  Purchase #6 $40.29   6.274%   $42.8178   $42.82   $42.80   $42.80  
  Purchase #7 $216.33   11.311%   $240.7991   $240.80   $240.80   $240.80  
  7 purchase totals = $1,050.87       $1,153.2327   $1,153.23   $1,153.20   $1,153.20