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 $63.80   9.166%   $69.6479   $69.65   $69.65   $69.60  
  Purchase #2 $148.87   8.224%   $161.1131   $161.11   $161.10   $161.10  
  Purchase #3 $83.97   3.197%   $86.6545   $86.65   $86.65   $86.70  
  Purchase #4 $159.81   9.779%   $175.4378   $175.44   $175.45   $175.40  
  Purchase #5 $194.28   9.491%   $212.7191   $212.72   $212.70   $212.70  
  Purchase #6 $218.45   9.319%   $238.8074   $238.81   $238.80   $238.80  
  Purchase #7 $75.52   10.211%   $83.2313   $83.23   $83.25   $83.20  
  7 purchase totals = $944.70       $1,027.6111   $1,027.61   $1,027.60   $1,027.50