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 $59.71   12.107%   $66.9391   $66.94   $66.95   $66.90  
  Purchase #2 $219.28   6.248%   $232.9806   $232.98   $233.00   $233.00  
  Purchase #3 $226.91   11.835%   $253.7648   $253.76   $253.75   $253.80  
  Purchase #4 $27.38   9.180%   $29.8935   $29.89   $29.90   $29.90  
  Purchase #5 $65.74   8.213%   $71.1392   $71.14   $71.15   $71.10  
  Purchase #6 $158.62   4.218%   $165.3106   $165.31   $165.30   $165.30  
  Purchase #7 $12.44   7.255%   $13.3425   $13.34   $13.35   $13.30  
  7 purchase totals = $770.08       $833.3703   $833.36   $833.40   $833.30