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 $237.53   9.502%   $260.1001   $260.10   $260.10   $260.10  
  Purchase #2 $147.66   6.813%   $157.7201   $157.72   $157.70   $157.70  
  Purchase #3 $162.59   11.817%   $181.8033   $181.80   $181.80   $181.80  
  Purchase #4 $181.97   9.401%   $199.077   $199.08   $199.10   $199.10  
  Purchase #5 $42.36   3.628%   $43.8968   $43.90   $43.90   $43.90  
  Purchase #6 $179.44   4.824%   $188.0962   $188.10   $188.10   $188.10  
  Purchase #7 $151.81   7.871%   $163.759   $163.76   $163.75   $163.80  
  7 purchase totals = $1,103.36       $1,194.4525   $1,194.46   $1,194.45   $1,194.50