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 $7.39   6.773%   $7.8905   $7.89   $7.90   $7.90  
  Purchase #2 $166.40   7.110%   $178.231   $178.23   $178.25   $178.20  
  Purchase #3 $172.34   3.830%   $178.9406   $178.94   $178.95   $178.90  
  Purchase #4 $38.52   4.125%   $40.109   $40.11   $40.10   $40.10  
  Purchase #5 $219.44   7.372%   $235.6171   $235.62   $235.60   $235.60  
  Purchase #6 $56.66   12.141%   $63.5391   $63.54   $63.55   $63.50  
  Purchase #7 $150.86   8.490%   $163.668   $163.67   $163.65   $163.70  
  7 purchase totals = $811.61       $867.9953   $868.00   $868.00   $867.90