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 $67.60   8.236%   $73.1675   $73.17   $73.15   $73.20  
  Purchase #2 $120.39   7.588%   $129.5252   $129.53   $129.55   $129.50  
  Purchase #3 $12.48   13.825%   $14.2054   $14.21   $14.20   $14.20  
  Purchase #4 $241.92   4.360%   $252.4677   $252.47   $252.45   $252.50  
  Purchase #5 $123.42   9.339%   $134.9462   $134.95   $134.95   $134.90  
  Purchase #6 $52.37   4.537%   $54.746   $54.75   $54.75   $54.70  
  Purchase #7 $154.82   7.139%   $165.8726   $165.87   $165.85   $165.90  
  7 purchase totals = $773.00       $824.9306   $824.95   $824.90   $824.90