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 $149.26   8.745%   $162.3128   $162.31   $162.30   $162.30  
  Purchase #2 $228.83   13.773%   $260.3468   $260.35   $260.35   $260.30  
  Purchase #3 $30.49   6.246%   $32.3944   $32.39   $32.40   $32.40  
  Purchase #4 $238.69   13.546%   $271.0229   $271.02   $271.00   $271.00  
  Purchase #5 $117.97   7.237%   $126.5075   $126.51   $126.50   $126.50  
  Purchase #6 $24.73   4.697%   $25.8916   $25.89   $25.90   $25.90  
  Purchase #7 $151.87   9.756%   $166.6864   $166.69   $166.70   $166.70  
  7 purchase totals = $941.84       $1,045.1624   $1,045.16   $1,045.15   $1,045.10