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 $32.92   10.127%   $36.2538   $36.25   $36.25   $36.30  
  Purchase #2 $219.57   3.678%   $227.6458   $227.65   $227.65   $227.60  
  Purchase #3 $36.98   12.840%   $41.7282   $41.73   $41.75   $41.70  
  Purchase #4 $174.77   3.742%   $181.3099   $181.31   $181.30   $181.30  
  Purchase #5 $120.75   12.369%   $135.6856   $135.69   $135.70   $135.70  
  Purchase #6 $133.32   11.833%   $149.0958   $149.10   $149.10   $149.10  
  Purchase #7 $230.58   13.694%   $262.1556   $262.16   $262.15   $262.20  
  7 purchase totals = $948.89       $1,033.8747   $1,033.89   $1,033.90   $1,033.90