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 $71.35   8.339%   $77.2999   $77.30   $77.30   $77.30  
  Purchase #2 $216.85   12.472%   $243.8955   $243.90   $243.90   $243.90  
  Purchase #3 $103.71   7.196%   $111.173   $111.17   $111.15   $111.20  
  Purchase #4 $195.57   7.872%   $210.9653   $210.97   $210.95   $211.00  
  Purchase #5 $8.78   10.475%   $9.6997   $9.70   $9.70   $9.70  
  Purchase #6 $129.88   3.248%   $134.0985   $134.10   $134.10   $134.10  
  Purchase #7 $13.55   8.790%   $14.741   $14.74   $14.75   $14.70  
  7 purchase totals = $739.69       $801.8729   $801.88   $801.85   $801.90