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 $196.33   7.461%   $210.9782   $210.98   $211.00   $211.00  
  Purchase #2 $136.60   12.351%   $153.4715   $153.47   $153.45   $153.50  
  Purchase #3 $148.52   3.714%   $154.036   $154.04   $154.05   $154.00  
  Purchase #4 $86.48   7.246%   $92.7463   $92.75   $92.75   $92.70  
  Purchase #5 $141.73   9.110%   $154.6416   $154.64   $154.65   $154.60  
  Purchase #6 $65.36   6.281%   $69.4653   $69.47   $69.45   $69.50  
  Purchase #7 $61.65   8.213%   $66.7133   $66.71   $66.70   $66.70  
  7 purchase totals = $836.67       $902.0522   $902.06   $902.05   $902.00