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 $228.49   9.520%   $250.2422   $250.24   $250.25   $250.20  
  Purchase #2 $111.65   7.347%   $119.8529   $119.85   $119.85   $119.90  
  Purchase #3 $162.44   5.265%   $170.9925   $170.99   $171.00   $171.00  
  Purchase #4 $142.64   4.631%   $149.2457   $149.25   $149.25   $149.20  
  Purchase #5 $59.77   6.223%   $63.4895   $63.49   $63.50   $63.50  
  Purchase #6 $174.62   9.118%   $190.5419   $190.54   $190.55   $190.50  
  Purchase #7 $180.77   8.570%   $196.262   $196.26   $196.25   $196.30  
  7 purchase totals = $1,060.38       $1,140.6267   $1,140.62   $1,140.65   $1,140.60