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 $77.98   4.578%   $81.5499   $81.55   $81.55   $81.50  
  Purchase #2 $195.41   9.318%   $213.6183   $213.62   $213.60   $213.60  
  Purchase #3 $123.37   5.579%   $130.2528   $130.25   $130.25   $130.30  
  Purchase #4 $221.95   5.597%   $234.3725   $234.37   $234.35   $234.40  
  Purchase #5 $160.32   9.356%   $175.3195   $175.32   $175.30   $175.30  
  Purchase #6 $143.57   6.575%   $153.0097   $153.01   $153.00   $153.00  
  Purchase #7 $68.57   5.317%   $72.2159   $72.22   $72.20   $72.20  
  7 purchase totals = $991.17       $1,060.3386   $1,060.34   $1,060.25   $1,060.30