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 $74.62   3.323%   $77.0996   $77.10   $77.10   $77.10  
  Purchase #2 $203.28   11.490%   $226.6369   $226.64   $226.65   $226.60  
  Purchase #3 $42.67   5.697%   $45.1009   $45.10   $45.10   $45.10  
  Purchase #4 $239.66   4.840%   $251.2595   $251.26   $251.25   $251.30  
  Purchase #5 $149.29   10.672%   $165.2222   $165.22   $165.20   $165.20  
  Purchase #6 $195.27   10.621%   $216.0096   $216.01   $216.00   $216.00  
  Purchase #7 $17.56   4.136%   $18.2863   $18.29   $18.30   $18.30  
  7 purchase totals = $922.35       $999.6150   $999.62   $999.60   $999.60