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 $188.28   3.264%   $194.4255   $194.43   $194.45   $194.40  
  Purchase #2 $98.97   7.561%   $106.4531   $106.45   $106.45   $106.50  
  Purchase #3 $15.58   11.369%   $17.3513   $17.35   $17.35   $17.40  
  Purchase #4 $226.97   13.678%   $258.015   $258.02   $258.00   $258.00  
  Purchase #5 $117.28   11.840%   $131.166   $131.17   $131.15   $131.20  
  Purchase #6 $125.88   13.313%   $142.6384   $142.64   $142.65   $142.60  
  Purchase #7 $207.91   11.191%   $231.1772   $231.18   $231.20   $231.20  
  7 purchase totals = $980.87       $1,081.2265   $1,081.24   $1,081.25   $1,081.30