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 $81.93   8.585%   $88.9637   $88.96   $88.95   $89.00  
  Purchase #2 $156.46   8.524%   $169.7967   $169.80   $169.80   $169.80  
  Purchase #3 $58.27   12.189%   $65.3725   $65.37   $65.35   $65.40  
  Purchase #4 $198.61   7.675%   $213.8533   $213.85   $213.85   $213.90  
  Purchase #5 $124.88   12.697%   $140.736   $140.74   $140.75   $140.70  
  Purchase #6 $23.65   11.737%   $26.4258   $26.43   $26.45   $26.40  
  Purchase #7 $89.47   6.294%   $95.1012   $95.10   $95.10   $95.10  
  7 purchase totals = $733.27       $800.2492   $800.25   $800.25   $800.30