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 $225.83   7.600%   $242.9931   $242.99   $243.00   $243.00  
  Purchase #2 $53.38   5.742%   $56.4451   $56.45   $56.45   $56.40  
  Purchase #3 $61.42   4.606%   $64.249   $64.25   $64.25   $64.20  
  Purchase #4 $168.52   6.730%   $179.8614   $179.86   $179.85   $179.90  
  Purchase #5 $177.30   13.143%   $200.6025   $200.60   $200.60   $200.60  
  Purchase #6 $96.68   4.110%   $100.6535   $100.65   $100.65   $100.70  
  Purchase #7 $246.38   4.345%   $257.0852   $257.09   $257.10   $257.10  
  7 purchase totals = $1,029.51       $1,101.8898   $1,101.89   $1,101.90   $1,101.90