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 $61.73   8.215%   $66.8011   $66.80   $66.80   $66.80  
  Purchase #2 $179.61   6.745%   $191.7247   $191.72   $191.70   $191.70  
  Purchase #3 $200.90   5.449%   $211.847   $211.85   $211.85   $211.80  
  Purchase #4 $165.27   7.174%   $177.1265   $177.13   $177.15   $177.10  
  Purchase #5 $182.86   11.618%   $204.1047   $204.10   $204.10   $204.10  
  Purchase #6 $238.37   5.663%   $251.8689   $251.87   $251.85   $251.90  
  Purchase #7 $11.66   11.509%   $13.0019   $13.00   $13.00   $13.00  
  7 purchase totals = $1,040.40       $1,116.4748   $1,116.47   $1,116.45   $1,116.40