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 $44.82   13.609%   $50.9196   $50.92   $50.90   $50.90  
  Purchase #2 $74.83   6.867%   $79.9686   $79.97   $79.95   $80.00  
  Purchase #3 $41.59   10.847%   $46.1013   $46.10   $46.10   $46.10  
  Purchase #4 $225.28   9.557%   $246.81   $246.81   $246.80   $246.80  
  Purchase #5 $76.70   8.249%   $83.027   $83.03   $83.05   $83.00  
  Purchase #6 $149.87   11.308%   $166.8173   $166.82   $166.80   $166.80  
  Purchase #7 $30.73   5.350%   $32.3741   $32.37   $32.35   $32.40  
  7 purchase totals = $643.82       $706.0179   $706.02   $705.95   $706.00