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 $182.63   12.747%   $205.9098   $205.91   $205.90   $205.90  
  Purchase #2 $230.97   12.427%   $259.6726   $259.67   $259.65   $259.70  
  Purchase #3 $96.97   10.850%   $107.4912   $107.49   $107.50   $107.50  
  Purchase #4 $43.35   5.845%   $45.8838   $45.88   $45.90   $45.90  
  Purchase #5 $109.80   11.840%   $122.8003   $122.80   $122.80   $122.80  
  Purchase #6 $23.31   5.488%   $24.5893   $24.59   $24.60   $24.60  
  Purchase #7 $119.36   11.684%   $133.306   $133.31   $133.30   $133.30  
  7 purchase totals = $806.39       $899.6530   $899.65   $899.65   $899.70