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 $244.93   5.608%   $258.6657   $258.67   $258.65   $258.70  
  Purchase #2 $107.94   11.518%   $120.3725   $120.37   $120.35   $120.40  
  Purchase #3 $49.88   11.285%   $55.509   $55.51   $55.50   $55.50  
  Purchase #4 $76.37   4.744%   $79.993   $79.99   $80.00   $80.00  
  Purchase #5 $12.92   8.235%   $13.984   $13.98   $14.00   $14.00  
  Purchase #6 $238.83   10.441%   $263.7662   $263.77   $263.75   $263.80  
  Purchase #7 $192.30   9.538%   $210.6416   $210.64   $210.65   $210.60  
  7 purchase totals = $923.17       $1,002.9320   $1,002.93   $1,002.90   $1,003.00