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 $198.77   9.474%   $217.6015   $217.60   $217.60   $217.60  
  Purchase #2 $151.59   12.212%   $170.1022   $170.10   $170.10   $170.10  
  Purchase #3 $66.51   3.348%   $68.7368   $68.74   $68.75   $68.70  
  Purchase #4 $249.93   3.416%   $258.4676   $258.47   $258.45   $258.50  
  Purchase #5 $82.75   9.391%   $90.5211   $90.52   $90.50   $90.50  
  Purchase #6 $182.96   10.409%   $202.0043   $202.00   $202.00   $202.00  
  Purchase #7 $245.41   7.644%   $264.1691   $264.17   $264.15   $264.20  
  7 purchase totals = $1,177.92       $1,271.6026   $1,271.60   $1,271.55   $1,271.60