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 $153.56   13.317%   $174.0096   $174.01   $174.00   $174.00  
  Purchase #2 $196.99   12.134%   $220.8928   $220.89   $220.90   $220.90  
  Purchase #3 $122.36   11.734%   $136.7177   $136.72   $136.70   $136.70  
  Purchase #4 $163.60   4.840%   $171.5182   $171.52   $171.50   $171.50  
  Purchase #5 $212.98   10.236%   $234.7806   $234.78   $234.80   $234.80  
  Purchase #6 $172.71   7.231%   $185.1987   $185.20   $185.20   $185.20  
  Purchase #7 $49.83   12.518%   $56.0677   $56.07   $56.05   $56.10  
  7 purchase totals = $1,072.03       $1,179.1853   $1,179.19   $1,179.15   $1,179.20