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 $205.98   13.851%   $234.5103   $234.51   $234.50   $234.50  
  Purchase #2 $136.97   13.638%   $155.65   $155.65   $155.65   $155.70  
  Purchase #3 $71.89   4.323%   $74.9978   $75.00   $75.00   $75.00  
  Purchase #4 $209.68   4.799%   $219.7425   $219.74   $219.75   $219.70  
  Purchase #5 $148.78   10.278%   $164.0716   $164.07   $164.05   $164.10  
  Purchase #6 $70.63   8.527%   $76.6526   $76.65   $76.65   $76.70  
  Purchase #7 $184.36   5.283%   $194.0997   $194.10   $194.10   $194.10  
  7 purchase totals = $1,028.29       $1,119.7245   $1,119.72   $1,119.70   $1,119.80