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 $236.29   12.641%   $266.1594   $266.16   $266.15   $266.20  
  Purchase #2 $98.67   5.545%   $104.1413   $104.14   $104.15   $104.10  
  Purchase #3 $158.94   7.252%   $170.4663   $170.47   $170.45   $170.50  
  Purchase #4 $96.95   9.306%   $105.9722   $105.97   $105.95   $106.00  
  Purchase #5 $218.48   5.731%   $231.0011   $231.00   $231.00   $231.00  
  Purchase #6 $228.96   6.816%   $244.5659   $244.57   $244.55   $244.60  
  Purchase #7 $65.49   13.530%   $74.3508   $74.35   $74.35   $74.40  
  7 purchase totals = $1,103.78       $1,196.6570   $1,196.66   $1,196.60   $1,196.80