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 $243.79   13.841%   $277.533   $277.53   $277.55   $277.50  
  Purchase #2 $138.34   9.368%   $151.2997   $151.30   $151.30   $151.30  
  Purchase #3 $103.64   13.806%   $117.9485   $117.95   $117.95   $117.90  
  Purchase #4 $27.46   12.700%   $30.9474   $30.95   $30.95   $30.90  
  Purchase #5 $126.38   9.822%   $138.793   $138.79   $138.80   $138.80  
  Purchase #6 $55.74   6.821%   $59.542   $59.54   $59.55   $59.50  
  Purchase #7 $231.70   3.620%   $240.0875   $240.09   $240.10   $240.10  
  7 purchase totals = $927.05       $1,016.1511   $1,016.15   $1,016.20   $1,016.00