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 $65.55   8.694%   $71.2489   $71.25   $71.25   $71.20  
  Purchase #2 $248.25   8.127%   $268.4253   $268.43   $268.45   $268.40  
  Purchase #3 $106.33   8.673%   $115.552   $115.55   $115.55   $115.60  
  Purchase #4 $175.51   9.825%   $192.7539   $192.75   $192.75   $192.80  
  Purchase #5 $182.58   4.676%   $191.1174   $191.12   $191.10   $191.10  
  Purchase #6 $107.48   3.244%   $110.9667   $110.97   $110.95   $111.00  
  Purchase #7 $193.59   5.338%   $203.9238   $203.92   $203.90   $203.90  
  7 purchase totals = $1,079.29       $1,153.9880   $1,153.99   $1,153.95   $1,154.00