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 $183.79   4.496%   $192.0532   $192.05   $192.05   $192.10  
  Purchase #2 $245.85   4.671%   $257.3337   $257.33   $257.35   $257.30  
  Purchase #3 $228.59   3.224%   $235.9597   $235.96   $235.95   $236.00  
  Purchase #4 $177.34   3.634%   $183.7845   $183.78   $183.80   $183.80  
  Purchase #5 $35.25   3.578%   $36.5112   $36.51   $36.50   $36.50  
  Purchase #6 $182.87   10.396%   $201.8812   $201.88   $201.90   $201.90  
  Purchase #7 $121.37   4.779%   $127.1703   $127.17   $127.15   $127.20  
  7 purchase totals = $1,175.06       $1,234.6938   $1,234.68   $1,234.70   $1,234.80