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 $41.25   10.661%   $45.6477   $45.65   $45.65   $45.60  
  Purchase #2 $247.71   10.396%   $273.4619   $273.46   $273.45   $273.50  
  Purchase #3 $17.32   3.675%   $17.9565   $17.96   $17.95   $18.00  
  Purchase #4 $92.39   7.442%   $99.2657   $99.27   $99.25   $99.30  
  Purchase #5 $32.80   11.526%   $36.5805   $36.58   $36.60   $36.60  
  Purchase #6 $131.60   5.865%   $139.3183   $139.32   $139.30   $139.30  
  Purchase #7 $117.90   3.338%   $121.8355   $121.84   $121.85   $121.80  
  7 purchase totals = $680.97       $734.0661   $734.08   $734.05   $734.10