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 $61.93   11.736%   $69.1981   $69.20   $69.20   $69.20  
  Purchase #2 $188.42   12.481%   $211.9367   $211.94   $211.95   $211.90  
  Purchase #3 $169.41   12.436%   $190.4778   $190.48   $190.50   $190.50  
  Purchase #4 $131.78   12.360%   $148.068   $148.07   $148.05   $148.10  
  Purchase #5 $118.80   7.152%   $127.2966   $127.30   $127.30   $127.30  
  Purchase #6 $14.94   5.272%   $15.7276   $15.73   $15.75   $15.70  
  Purchase #7 $117.86   5.348%   $124.1632   $124.16   $124.15   $124.20  
  7 purchase totals = $803.14       $886.8680   $886.88   $886.90   $886.90