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 $202.43   3.658%   $209.8349   $209.83   $209.85   $209.80  
  Purchase #2 $153.34   5.402%   $161.6234   $161.62   $161.60   $161.60  
  Purchase #3 $250.95   6.288%   $266.7297   $266.73   $266.75   $266.70  
  Purchase #4 $110.76   6.403%   $117.852   $117.85   $117.85   $117.90  
  Purchase #5 $14.50   11.841%   $16.2169   $16.22   $16.20   $16.20  
  Purchase #6 $153.73   12.645%   $173.1692   $173.17   $173.15   $173.20  
  Purchase #7 $223.28   4.594%   $233.5375   $233.54   $233.55   $233.50  
  7 purchase totals = $1,108.99       $1,178.9636   $1,178.96   $1,178.95   $1,178.90