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 $96.37   7.448%   $103.5476   $103.55   $103.55   $103.50  
  Purchase #2 $221.64   11.151%   $246.3551   $246.36   $246.35   $246.40  
  Purchase #3 $165.88   8.737%   $180.3729   $180.37   $180.35   $180.40  
  Purchase #4 $191.67   11.532%   $213.7734   $213.77   $213.75   $213.80  
  Purchase #5 $16.72   3.808%   $17.3567   $17.36   $17.35   $17.40  
  Purchase #6 $27.26   12.404%   $30.6413   $30.64   $30.65   $30.60  
  Purchase #7 $218.73   6.445%   $232.8271   $232.83   $232.85   $232.80  
  7 purchase totals = $938.27       $1,024.8741   $1,024.88   $1,024.85   $1,024.90