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 $29.60   9.450%   $32.3972   $32.40   $32.40   $32.40  
  Purchase #2 $19.89   13.455%   $22.5662   $22.57   $22.55   $22.60  
  Purchase #3 $203.86   3.315%   $210.618   $210.62   $210.60   $210.60  
  Purchase #4 $231.99   4.533%   $242.5061   $242.51   $242.50   $242.50  
  Purchase #5 $193.97   5.174%   $204.006   $204.01   $204.00   $204.00  
  Purchase #6 $239.89   12.117%   $268.9575   $268.96   $268.95   $269.00  
  Purchase #7 $74.87   12.496%   $84.2258   $84.23   $84.25   $84.20  
  7 purchase totals = $994.07       $1,065.2768   $1,065.30   $1,065.25   $1,065.30