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 $61.98   13.497%   $70.3454   $70.35   $70.35   $70.30  
  Purchase #2 $5.83   6.646%   $6.2175   $6.22   $6.20   $6.20  
  Purchase #3 $171.59   6.575%   $182.872   $182.87   $182.85   $182.90  
  Purchase #4 $91.70   8.814%   $99.7824   $99.78   $99.80   $99.80  
  Purchase #5 $50.68   12.643%   $57.0875   $57.09   $57.10   $57.10  
  Purchase #6 $177.43   5.746%   $187.6251   $187.63   $187.65   $187.60  
  Purchase #7 $90.98   9.513%   $99.6349   $99.63   $99.65   $99.60  
  7 purchase totals = $650.19       $703.5648   $703.57   $703.60   $703.50