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 $191.65   4.122%   $199.5498   $199.55   $199.55   $199.50  
  Purchase #2 $75.33   4.650%   $78.8328   $78.83   $78.85   $78.80  
  Purchase #3 $60.91   13.338%   $69.0342   $69.03   $69.05   $69.00  
  Purchase #4 $118.41   3.334%   $122.3578   $122.36   $122.35   $122.40  
  Purchase #5 $217.66   5.246%   $229.0784   $229.08   $229.10   $229.10  
  Purchase #6 $204.95   13.197%   $231.9973   $232.00   $232.00   $232.00  
  Purchase #7 $181.86   13.265%   $205.9837   $205.98   $206.00   $206.00  
  7 purchase totals = $1,050.77       $1,136.8340   $1,136.83   $1,136.90   $1,136.80