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 $82.98   12.665%   $93.4894   $93.49   $93.50   $93.50  
  Purchase #2 $210.47   3.168%   $217.1377   $217.14   $217.15   $217.10  
  Purchase #3 $181.78   6.215%   $193.0776   $193.08   $193.10   $193.10  
  Purchase #4 $95.33   11.189%   $105.9965   $106.00   $106.00   $106.00  
  Purchase #5 $154.60   3.267%   $159.6508   $159.65   $159.65   $159.70  
  Purchase #6 $61.95   8.127%   $66.9847   $66.98   $67.00   $67.00  
  Purchase #7 $220.76   11.727%   $246.6485   $246.65   $246.65   $246.60  
  7 purchase totals = $1,007.87       $1,082.9852   $1,082.99   $1,083.05   $1,083.00