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 $186.70   13.717%   $212.3096   $212.31   $212.30   $212.30  
  Purchase #2 $163.28   11.243%   $181.6376   $181.64   $181.65   $181.60  
  Purchase #3 $185.70   6.163%   $197.1447   $197.14   $197.15   $197.10  
  Purchase #4 $236.61   6.620%   $252.2736   $252.27   $252.25   $252.30  
  Purchase #5 $134.64   9.214%   $147.0457   $147.05   $147.05   $147.00  
  Purchase #6 $68.89   8.495%   $74.7422   $74.74   $74.75   $74.70  
  Purchase #7 $146.46   13.812%   $166.6891   $166.69   $166.70   $166.70  
  7 purchase totals = $1,122.28       $1,231.8425   $1,231.84   $1,231.85   $1,231.70