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 $62.78   8.822%   $68.3185   $68.32   $68.30   $68.30  
  Purchase #2 $96.41   4.518%   $100.7658   $100.77   $100.75   $100.80  
  Purchase #3 $211.47   6.351%   $224.9005   $224.90   $224.90   $224.90  
  Purchase #4 $242.33   6.158%   $257.2527   $257.25   $257.25   $257.30  
  Purchase #5 $48.58   4.752%   $50.8885   $50.89   $50.90   $50.90  
  Purchase #6 $11.31   12.488%   $12.7224   $12.72   $12.70   $12.70  
  Purchase #7 $145.79   11.803%   $162.9976   $163.00   $163.00   $163.00  
  7 purchase totals = $818.67       $877.8460   $877.85   $877.80   $877.90