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 $63.33   10.179%   $69.7764   $69.78   $69.80   $69.80  
  Purchase #2 $217.28   10.807%   $240.7614   $240.76   $240.75   $240.80  
  Purchase #3 $83.36   12.620%   $93.88   $93.88   $93.90   $93.90  
  Purchase #4 $20.51   5.121%   $21.5603   $21.56   $21.55   $21.60  
  Purchase #5 $246.85   11.694%   $275.7166   $275.72   $275.70   $275.70  
  Purchase #6 $221.54   10.121%   $243.9621   $243.96   $243.95   $244.00  
  Purchase #7 $56.85   7.180%   $60.9318   $60.93   $60.95   $60.90  
  7 purchase totals = $909.72       $1,006.5886   $1,006.59   $1,006.60   $1,006.70