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 $212.85   13.475%   $241.5315   $241.53   $241.55   $241.50  
  Purchase #2 $38.97   5.869%   $41.2571   $41.26   $41.25   $41.30  
  Purchase #3 $224.66   9.324%   $245.6073   $245.61   $245.60   $245.60  
  Purchase #4 $92.40   6.625%   $98.5215   $98.52   $98.50   $98.50  
  Purchase #5 $79.60   6.239%   $84.5662   $84.57   $84.55   $84.60  
  Purchase #6 $172.89   9.751%   $189.7485   $189.75   $189.75   $189.70  
  Purchase #7 $150.69   3.587%   $156.0953   $156.10   $156.10   $156.10  
  7 purchase totals = $972.06       $1,057.3274   $1,057.34   $1,057.30   $1,057.30