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 $184.97   5.194%   $194.5773   $194.58   $194.60   $194.60  
  Purchase #2 $117.35   5.764%   $124.1141   $124.11   $124.10   $124.10  
  Purchase #3 $170.44   11.687%   $190.3593   $190.36   $190.35   $190.40  
  Purchase #4 $54.63   3.120%   $56.3345   $56.33   $56.35   $56.30  
  Purchase #5 $10.39   10.434%   $11.4741   $11.47   $11.45   $11.50  
  Purchase #6 $126.35   6.142%   $134.1104   $134.11   $134.10   $134.10  
  Purchase #7 $58.80   12.309%   $66.0377   $66.04   $66.05   $66.00  
  7 purchase totals = $722.93       $777.0074   $777.00   $777.00   $777.00