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 $238.36   3.136%   $245.835   $245.84   $245.85   $245.80  
  Purchase #2 $171.52   8.481%   $186.0666   $186.07   $186.05   $186.10  
  Purchase #3 $207.87   4.108%   $216.4093   $216.41   $216.40   $216.40  
  Purchase #4 $237.75   10.651%   $263.0728   $263.07   $263.05   $263.10  
  Purchase #5 $184.96   7.532%   $198.8912   $198.89   $198.90   $198.90  
  Purchase #6 $207.26   8.537%   $224.9538   $224.95   $224.95   $225.00  
  Purchase #7 $131.31   7.605%   $141.2961   $141.30   $141.30   $141.30  
  7 purchase totals = $1,379.03       $1,476.5248   $1,476.53   $1,476.50   $1,476.60