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 $188.95   9.447%   $206.8001   $206.80   $206.80   $206.80  
  Purchase #2 $197.50   13.597%   $224.3541   $224.35   $224.35   $224.40  
  Purchase #3 $71.80   6.331%   $76.3457   $76.35   $76.35   $76.30  
  Purchase #4 $238.59   7.360%   $256.1502   $256.15   $256.15   $256.20  
  Purchase #5 $97.57   4.550%   $102.0094   $102.01   $102.00   $102.00  
  Purchase #6 $167.31   7.268%   $179.4701   $179.47   $179.45   $179.50  
  Purchase #7 $188.82   10.471%   $208.5913   $208.59   $208.60   $208.60  
  7 purchase totals = $1,150.54       $1,253.7209   $1,253.72   $1,253.70   $1,253.80