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 $64.68   3.222%   $66.764   $66.76   $66.75   $66.80  
  Purchase #2 $228.31   5.396%   $240.6296   $240.63   $240.65   $240.60  
  Purchase #3 $11.68   3.425%   $12.08   $12.08   $12.10   $12.10  
  Purchase #4 $210.53   6.754%   $224.7492   $224.75   $224.75   $224.70  
  Purchase #5 $100.30   3.691%   $104.0021   $104.00   $104.00   $104.00  
  Purchase #6 $5.48   8.534%   $5.9477   $5.95   $5.95   $5.90  
  Purchase #7 $188.27   7.596%   $202.571   $202.57   $202.55   $202.60  
  7 purchase totals = $809.25       $856.7436   $856.74   $856.75   $856.70