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 $94.37   12.547%   $106.2106   $106.21   $106.20   $106.20  
  Purchase #2 $52.98   9.337%   $57.9267   $57.93   $57.95   $57.90  
  Purchase #3 $196.74   5.562%   $207.6827   $207.68   $207.70   $207.70  
  Purchase #4 $173.72   3.542%   $179.8732   $179.87   $179.85   $179.90  
  Purchase #5 $38.55   10.620%   $42.644   $42.64   $42.65   $42.60  
  Purchase #6 $154.32   8.112%   $166.8384   $166.84   $166.85   $166.80  
  Purchase #7 $39.76   9.214%   $43.4235   $43.42   $43.40   $43.40  
  7 purchase totals = $750.44       $804.5991   $804.59   $804.60   $804.50