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 $116.25   13.566%   $132.0205   $132.02   $132.00   $132.00  
  Purchase #2 $46.68   3.111%   $48.1322   $48.13   $48.15   $48.10  
  Purchase #3 $126.33   9.681%   $138.56   $138.56   $138.55   $138.60  
  Purchase #4 $195.64   13.291%   $221.6425   $221.64   $221.65   $221.60  
  Purchase #5 $231.61   9.568%   $253.7704   $253.77   $253.75   $253.80  
  Purchase #6 $92.87   9.490%   $101.6834   $101.68   $101.70   $101.70  
  Purchase #7 $170.34   6.724%   $181.7937   $181.79   $181.80   $181.80  
  7 purchase totals = $979.72       $1,077.6027   $1,077.59   $1,077.60   $1,077.60