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 $63.48   8.712%   $69.0104   $69.01   $69.00   $69.00  
  Purchase #2 $214.88   13.297%   $243.4526   $243.45   $243.45   $243.50  
  Purchase #3 $81.65   4.417%   $85.2565   $85.26   $85.25   $85.30  
  Purchase #4 $114.68   3.346%   $118.5172   $118.52   $118.50   $118.50  
  Purchase #5 $57.52   11.268%   $64.0014   $64.00   $64.00   $64.00  
  Purchase #6 $53.34   12.811%   $60.1734   $60.17   $60.15   $60.20  
  Purchase #7 $30.69   3.650%   $31.8102   $31.81   $31.80   $31.80  
  7 purchase totals = $616.24       $672.2217   $672.22   $672.15   $672.30