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 $218.59   8.682%   $237.568   $237.57   $237.55   $237.60  
  Purchase #2 $56.26   9.294%   $61.4888   $61.49   $61.50   $61.50  
  Purchase #3 $178.46   5.715%   $188.659   $188.66   $188.65   $188.70  
  Purchase #4 $206.90   3.258%   $213.6408   $213.64   $213.65   $213.60  
  Purchase #5 $234.77   7.539%   $252.4693   $252.47   $252.45   $252.50  
  Purchase #6 $127.30   7.684%   $137.0817   $137.08   $137.10   $137.10  
  Purchase #7 $68.98   8.701%   $74.9819   $74.98   $75.00   $75.00  
  7 purchase totals = $1,091.26       $1,165.8895   $1,165.89   $1,165.90   $1,166.00