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 $59.40   3.776%   $61.6429   $61.64   $61.65   $61.60  
  Purchase #2 $145.47   13.392%   $164.9513   $164.95   $164.95   $165.00  
  Purchase #3 $157.48   9.178%   $171.9335   $171.93   $171.95   $171.90  
  Purchase #4 $75.86   12.412%   $85.2757   $85.28   $85.30   $85.30  
  Purchase #5 $246.70   12.549%   $277.6584   $277.66   $277.65   $277.70  
  Purchase #6 $68.48   9.792%   $75.1856   $75.19   $75.20   $75.20  
  Purchase #7 $235.92   7.471%   $253.5456   $253.55   $253.55   $253.50  
  7 purchase totals = $989.31       $1,090.1930   $1,090.20   $1,090.25   $1,090.20