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 $235.92   13.617%   $268.0452   $268.05   $268.05   $268.00  
  Purchase #2 $198.95   7.283%   $213.4395   $213.44   $213.45   $213.40  
  Purchase #3 $60.92   8.833%   $66.3011   $66.30   $66.30   $66.30  
  Purchase #4 $227.27   10.736%   $251.6697   $251.67   $251.65   $251.70  
  Purchase #5 $40.67   12.797%   $45.8745   $45.87   $45.85   $45.90  
  Purchase #6 $158.55   11.710%   $177.1162   $177.12   $177.10   $177.10  
  Purchase #7 $42.75   7.320%   $45.8793   $45.88   $45.90   $45.90  
  7 purchase totals = $965.03       $1,068.3255   $1,068.33   $1,068.30   $1,068.30