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 $31.52   11.155%   $35.0361   $35.04   $35.05   $35.00  
  Purchase #2 $212.60   11.584%   $237.2276   $237.23   $237.25   $237.20  
  Purchase #3 $80.81   3.279%   $83.4598   $83.46   $83.45   $83.50  
  Purchase #4 $167.29   5.177%   $175.9506   $175.95   $175.95   $176.00  
  Purchase #5 $72.37   10.518%   $79.9819   $79.98   $80.00   $80.00  
  Purchase #6 $136.87   13.146%   $154.8629   $154.86   $154.85   $154.90  
  Purchase #7 $161.37   9.436%   $176.5969   $176.60   $176.60   $176.60  
  7 purchase totals = $862.83       $943.1158   $943.12   $943.15   $943.20