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 $202.39   8.835%   $220.2712   $220.27   $220.25   $220.30  
  Purchase #2 $214.42   8.823%   $233.3383   $233.34   $233.35   $233.30  
  Purchase #3 $219.76   5.802%   $232.5105   $232.51   $232.50   $232.50  
  Purchase #4 $81.59   8.309%   $88.3693   $88.37   $88.35   $88.40  
  Purchase #5 $125.38   9.575%   $137.3851   $137.39   $137.40   $137.40  
  Purchase #6 $167.54   10.755%   $185.5589   $185.56   $185.55   $185.60  
  Purchase #7 $20.84   5.662%   $22.02   $22.02   $22.00   $22.00  
  7 purchase totals = $1,031.92       $1,119.4533   $1,119.46   $1,119.40   $1,119.50