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 $101.77   8.228%   $110.1436   $110.14   $110.15   $110.10  
  Purchase #2 $20.73   8.317%   $22.4541   $22.45   $22.45   $22.50  
  Purchase #3 $113.93   8.353%   $123.4466   $123.45   $123.45   $123.40  
  Purchase #4 $165.34   5.164%   $173.8782   $173.88   $173.90   $173.90  
  Purchase #5 $232.77   7.406%   $250.0089   $250.01   $250.00   $250.00  
  Purchase #6 $222.93   8.661%   $242.238   $242.24   $242.25   $242.20  
  Purchase #7 $119.85   8.574%   $130.1259   $130.13   $130.15   $130.10  
  7 purchase totals = $977.32       $1,052.2953   $1,052.30   $1,052.35   $1,052.20