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 $204.44   13.721%   $232.4912   $232.49   $232.50   $232.50  
  Purchase #2 $116.99   5.599%   $123.5403   $123.54   $123.55   $123.50  
  Purchase #3 $7.71   7.185%   $8.264   $8.26   $8.25   $8.30  
  Purchase #4 $111.60   7.382%   $119.8383   $119.84   $119.85   $119.80  
  Purchase #5 $241.85   10.363%   $266.9129   $266.91   $266.90   $266.90  
  Purchase #6 $76.29   6.177%   $81.0024   $81.00   $81.00   $81.00  
  Purchase #7 $183.56   10.557%   $202.9384   $202.94   $202.95   $202.90  
  7 purchase totals = $942.44       $1,034.9875   $1,034.98   $1,035.00   $1,034.90