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 $60.99   6.803%   $65.1391   $65.14   $65.15   $65.10  
  Purchase #2 $167.34   3.472%   $173.15   $173.15   $173.15   $173.20  
  Purchase #3 $19.47   12.665%   $21.9359   $21.94   $21.95   $21.90  
  Purchase #4 $243.89   8.457%   $264.5158   $264.52   $264.50   $264.50  
  Purchase #5 $11.46   4.690%   $11.9975   $12.00   $12.00   $12.00  
  Purchase #6 $85.56   13.492%   $97.1038   $97.10   $97.10   $97.10  
  Purchase #7 $128.53   4.818%   $134.7226   $134.72   $134.70   $134.70  
  7 purchase totals = $717.24       $768.5647   $768.57   $768.55   $768.50