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 $24.34   7.813%   $26.2417   $26.24   $26.25   $26.20  
  Purchase #2 $132.92   6.140%   $141.0813   $141.08   $141.10   $141.10  
  Purchase #3 $240.60   8.423%   $260.8657   $260.87   $260.85   $260.90  
  Purchase #4 $153.28   5.247%   $161.3226   $161.32   $161.30   $161.30  
  Purchase #5 $206.52   8.821%   $224.7371   $224.74   $224.75   $224.70  
  Purchase #6 $27.49   11.554%   $30.6662   $30.67   $30.65   $30.70  
  Purchase #7 $207.81   7.722%   $223.8571   $223.86   $223.85   $223.90  
  7 purchase totals = $992.96       $1,068.7717   $1,068.78   $1,068.75   $1,068.80