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 $248.91   5.870%   $263.521   $263.52   $263.50   $263.50  
  Purchase #2 $65.56   8.335%   $71.0244   $71.02   $71.00   $71.00  
  Purchase #3 $12.34   7.392%   $13.2522   $13.25   $13.25   $13.30  
  Purchase #4 $235.32   4.239%   $245.2952   $245.30   $245.30   $245.30  
  Purchase #5 $102.73   12.381%   $115.449   $115.45   $115.45   $115.40  
  Purchase #6 $217.95   6.166%   $231.3888   $231.39   $231.40   $231.40  
  Purchase #7 $181.72   5.531%   $191.7709   $191.77   $191.75   $191.80  
  7 purchase totals = $1,064.53       $1,131.7015   $1,131.70   $1,131.65   $1,131.70