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 $14.98   10.687%   $16.5809   $16.58   $16.60   $16.60  
  Purchase #2 $243.65   5.336%   $256.6512   $256.65   $256.65   $256.70  
  Purchase #3 $16.77   9.327%   $18.3341   $18.33   $18.35   $18.30  
  Purchase #4 $193.38   4.822%   $202.7048   $202.70   $202.70   $202.70  
  Purchase #5 $219.75   3.693%   $227.8654   $227.87   $227.85   $227.90  
  Purchase #6 $65.51   11.734%   $73.1969   $73.20   $73.20   $73.20  
  Purchase #7 $55.72   10.232%   $61.4213   $61.42   $61.40   $61.40  
  7 purchase totals = $809.76       $856.7546   $856.75   $856.75   $856.80