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 $156.52   4.238%   $163.1533   $163.15   $163.15   $163.20  
  Purchase #2 $157.67   4.209%   $164.3063   $164.31   $164.30   $164.30  
  Purchase #3 $238.31   3.375%   $246.353   $246.35   $246.35   $246.40  
  Purchase #4 $115.92   3.115%   $119.5309   $119.53   $119.55   $119.50  
  Purchase #5 $67.60   3.454%   $69.9349   $69.93   $69.95   $69.90  
  Purchase #6 $124.68   6.634%   $132.9513   $132.95   $132.95   $133.00  
  Purchase #7 $166.40   8.141%   $179.9466   $179.95   $179.95   $179.90  
  7 purchase totals = $1,027.10       $1,076.1763   $1,076.17   $1,076.20   $1,076.20