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 $190.80   6.272%   $202.767   $202.77   $202.75   $202.80  
  Purchase #2 $65.80   10.621%   $72.7886   $72.79   $72.80   $72.80  
  Purchase #3 $218.81   8.342%   $237.0631   $237.06   $237.05   $237.10  
  Purchase #4 $242.32   5.847%   $256.4885   $256.49   $256.50   $256.50  
  Purchase #5 $62.97   11.119%   $69.9716   $69.97   $69.95   $70.00  
  Purchase #6 $133.50   9.280%   $145.8888   $145.89   $145.90   $145.90  
  Purchase #7 $97.78   13.469%   $110.95   $110.95   $110.95   $111.00  
  7 purchase totals = $1,011.98       $1,095.9176   $1,095.92   $1,095.90   $1,096.10